ZFS sync / ZIL clarification

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ZFS sync / ZIL clarification

Mark Felder-4
I believe I was told something misleading a few weeks ago and I'd like to  
have this officially clarified.

NFS on ZFS is horrible unless you have sync = disabled. I was told this  
was effectively disabling the ZIL, which is of course naughty. Now I  
stumbled upon this tonight:


> Just for the archives... sync=disabled won't disable disable the zil,
> it'll disable waiting for a disk-flush on fsync etc. With a battery
> backed controller cache, those flushes should go to cache, and bepretty  
> mich free. You end up tossing away something for nothing.

Is this accurate?
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Re: ZFS sync / ZIL clarification

Peter Maloney
On 01/30/2012 05:30 AM, Mark Felder wrote:
> I believe I was told something misleading a few weeks ago and I'd like
> to have this officially clarified.
>
> NFS on ZFS is horrible unless you have sync = disabled.
With ESXi = true
with others = depends on your definition of horrible

> I was told this was effectively disabling the ZIL, which is of course
> naughty. Now I stumbled upon this tonight:
>
true only for the specific dataset you specified
eg.
zfs set sync=disabled tank/esxi

>> Just for the archives... sync=disabled won't disable disable the
>> zil,it'll disable waiting for a disk-flush on fsync etc.
Same thing... "waiting for a disk-flush" is the only time the ZIL is
used, from what I understand.

>> With a batterybacked controller cache, those flushes should go to
>> cache, and bepretty mich free. You end up tossing away something for
>> nothing.
False I guess. Would be nice, but how do you battery back your RAM,
which ZFS uses as a write cache? (If you know something I don't know,
please share.)
>
> Is this accurate?

sync=disabled caused data corruption for me. So you need to have battery
backed cache... unfortunately, the cache we are talking about is in RAM,
not your IO controller. So put a UPS on there, and you are safe except
when you get a kernel panic (which is what happened to cause my
corruption). But if you get something like the Gigabyte iRAM or the
Acard ANS-9010
<http://www.acard.com.tw/english/fb01-product.jsp?prod_no=ANS-9010&type1_title=%20Solid%20State%20Drive&idno_no=270>,
set it as your ZIL, and leave sync=standard, you should be safer. (I
don't know if the iRAM works in FreeBSD, but someone
<http://christopher-technicalmusings.blogspot.com/2011/06/speeding-up-freebsds-nfs-on-zfs-for-esx.html>
told me he uses the ANS-9010)

And NFS with ZFS is not horrible, except with ESXi's built in NFS client
it uses for datastores.  (the same someone that said he uses the
ANS-9010 also provides a 'patch' for the FreeBSD NFS server that
disables ESXi's stupid behavior, without disabling sync entirely, but
also possibly disables it for others that use it responsibly [a database
perhaps])

here
<http://www.citi.umich.edu/projects/nfs-perf/results/cel/write-throughput.html>
is a fantastic study about NFS; dunno if this study resulted in patches
now in use or not, or how old it is [newest reference is 2002, so at
most 10 years old]. In my experience, the write caching in use today
still sucks. If I run async with sync=disabled, I can still see a huge
improvement (20% on large files, up to 100% for smaller files <200MB)
using an ESXi virtual disk (with ext4 doing write caching) compared to
NFS directly.


Here begins the rant about ESXi, which may be off topic:

ESXi goes 7 MB/s with an SSD ZIL at 100% load, and 80 MB/s with a
ramdisk ZIL at 100% load (pathetic!),
something I can't reproduce (thought it was just a normal Linux client
with "-o sync" over 10 Gbps ethernet) got over 70MB/s with the ZIL at
70-90% load,
and other clients set to "-o sync,noatime,..." or "-o noatime,..."with
the ZIL only randomly 0-5% load, but go faster than 100 MB/s. I didn't
test "async", and without "sync", they seem to go the same speed.
setting sync=disabled always goes around 100 MB/s, and changes the load
on the ZIL to 0%.

The thing I can't reproduce might have been only possible on a pool that
I created with FreeBSD 8.2-RELEASE and then upgraded, which I no longer
have. Or maybe it was with "sync" without "noatime".

I am going to test with 9000 MTU, and if it is not much faster, I am
giving up on NFS. My original plan was to use ESXi with a ZFS datastore
with a replicated backup. That works terribly using the ESXi NFS client.
Netbooting the OSses to bypass the ESXi client works much better, but
still not good enough for many servers. NFS is poorly implemented, with
terrible write caching on the client side. Now my plan is to use FreeBSD
with VirtualBox and ZFS all in one system, and send replication
snapshots from there. I wanted to use ESXi, but I guess I can't.

And the worst thing about ESXi, is if you have 1 client going 7MB/s, the
second client has to share that 7MB/s, and non-ESXi clients will still
go horribly slow. If you have 10 non-ESXi clients going at 100 MB/s,
each one is limited to around 100 MB/s (again I only tested this with
1500 MTU so far), but together they can write much more.

Just now I tested 2 clients writing 100+100 MB/s (reported by GNU dd),
and 3 writing 50+60+60 MB/s (reported by GNU dd)
Output from "zpool iostat 5":
two clients:
tank        38.7T  4.76T      0  1.78K  25.5K   206M (matches 100+100)
three clients:
tank        38.7T  4.76T      1  2.44K   205K   245M (does not match
60+60+50)

(one client is a Linux netboot, and the others are using the Linux NFS
client)

But I am not an 'official', so this cannot be considered 'officially
clarified' ;)


> _______________________________________________
> [hidden email] mailing list
> http://lists.freebsd.org/mailman/listinfo/freebsd-fs
> To unsubscribe, send any mail to "[hidden email]"


--

--------------------------------------------
Peter Maloney
Brockmann Consult
Max-Planck-Str. 2
21502 Geesthacht
Germany
Tel: +49 4152 889 300
Fax: +49 4152 889 333
E-mail: [hidden email]
Internet: http://www.brockmann-consult.de
--------------------------------------------

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Re: ZFS sync / ZIL clarification

Mark Felder-4
Thanks Peter. You're also confirming my original suspicions and the  
results of my testing.

I'm going to continue forward with this ZFS SAN backend for ESXi project  
with iSCSI via istgt, which actually works surprisingly well.

Honestly, NFS would have been quite useful, but it never would have made  
sense in our environment because you can't properly multipath to it  
without pNFS / NFS 4.1, which isn't available in FreeBSD yet and will take  
some time to prove its stability anyway.
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Re: ZFS sync / ZIL clarification

Dennis Glatting-4
In reply to this post by Peter Maloney
On Mon, 2012-01-30 at 08:47 +0100, Peter Maloney wrote:

> On 01/30/2012 05:30 AM, Mark Felder wrote:
> > I believe I was told something misleading a few weeks ago and I'd like
> > to have this officially clarified.
> >
> > NFS on ZFS is horrible unless you have sync = disabled.
> With ESXi = true
> with others = depends on your definition of horrible
>
> > I was told this was effectively disabling the ZIL, which is of course
> > naughty. Now I stumbled upon this tonight:
> >
> true only for the specific dataset you specified
> eg.
> zfs set sync=disabled tank/esxi
>
> >> Just for the archives... sync=disabled won't disable disable the
> >> zil,it'll disable waiting for a disk-flush on fsync etc.
> Same thing... "waiting for a disk-flush" is the only time the ZIL is
> used, from what I understand.
>
> >> With a batterybacked controller cache, those flushes should go to
> >> cache, and bepretty mich free. You end up tossing away something for
> >> nothing.
> False I guess. Would be nice, but how do you battery back your RAM,
> which ZFS uses as a write cache? (If you know something I don't know,
> please share.)
> >
> > Is this accurate?
>
> sync=disabled caused data corruption for me. So you need to have battery
> backed cache... unfortunately, the cache we are talking about is in RAM,
> not your IO controller. So put a UPS on there, and you are safe except
> when you get a kernel panic (which is what happened to cause my
> corruption). But if you get something like the Gigabyte iRAM or the
> Acard ANS-9010
> <http://www.acard.com.tw/english/fb01-product.jsp?prod_no=ANS-9010&type1_title=%20Solid%20State%20Drive&idno_no=270>,
> set it as your ZIL, and leave sync=standard, you should be safer. (I
> don't know if the iRAM works in FreeBSD, but someone
> <http://christopher-technicalmusings.blogspot.com/2011/06/speeding-up-freebsds-nfs-on-zfs-for-esx.html>
> told me he uses the ANS-9010)
>
> And NFS with ZFS is not horrible, except with ESXi's built in NFS client
> it uses for datastores.  (the same someone that said he uses the
> ANS-9010 also provides a 'patch' for the FreeBSD NFS server that
> disables ESXi's stupid behavior, without disabling sync entirely, but
> also possibly disables it for others that use it responsibly [a database
> perhaps])
>
> here
> <http://www.citi.umich.edu/projects/nfs-perf/results/cel/write-throughput.html>
> is a fantastic study about NFS; dunno if this study resulted in patches
> now in use or not, or how old it is [newest reference is 2002, so at
> most 10 years old]. In my experience, the write caching in use today
> still sucks. If I run async with sync=disabled, I can still see a huge
> improvement (20% on large files, up to 100% for smaller files <200MB)
> using an ESXi virtual disk (with ext4 doing write caching) compared to
> NFS directly.
>
>
> Here begins the rant about ESXi, which may be off topic:
>

ESXi 3.5, 4.0, 4.1, 5.0, or all of the above?


> ESXi goes 7 MB/s with an SSD ZIL at 100% load, and 80 MB/s with a
> ramdisk ZIL at 100% load (pathetic!),
> something I can't reproduce (thought it was just a normal Linux client
> with "-o sync" over 10 Gbps ethernet) got over 70MB/s with the ZIL at
> 70-90% load,
> and other clients set to "-o sync,noatime,..." or "-o noatime,..."with
> the ZIL only randomly 0-5% load, but go faster than 100 MB/s. I didn't
> test "async", and without "sync", they seem to go the same speed.
> setting sync=disabled always goes around 100 MB/s, and changes the load
> on the ZIL to 0%.
>
> The thing I can't reproduce might have been only possible on a pool that
> I created with FreeBSD 8.2-RELEASE and then upgraded, which I no longer
> have. Or maybe it was with "sync" without "noatime".
>
> I am going to test with 9000 MTU, and if it is not much faster, I am
> giving up on NFS. My original plan was to use ESXi with a ZFS datastore
> with a replicated backup. That works terribly using the ESXi NFS client.
> Netbooting the OSses to bypass the ESXi client works much better, but
> still not good enough for many servers. NFS is poorly implemented, with
> terrible write caching on the client side. Now my plan is to use FreeBSD
> with VirtualBox and ZFS all in one system, and send replication
> snapshots from there. I wanted to use ESXi, but I guess I can't.
>
> And the worst thing about ESXi, is if you have 1 client going 7MB/s, the
> second client has to share that 7MB/s, and non-ESXi clients will still
> go horribly slow. If you have 10 non-ESXi clients going at 100 MB/s,
> each one is limited to around 100 MB/s (again I only tested this with
> 1500 MTU so far), but together they can write much more.
>
> Just now I tested 2 clients writing 100+100 MB/s (reported by GNU dd),
> and 3 writing 50+60+60 MB/s (reported by GNU dd)
> Output from "zpool iostat 5":
> two clients:
> tank        38.7T  4.76T      0  1.78K  25.5K   206M (matches 100+100)
> three clients:
> tank        38.7T  4.76T      1  2.44K   205K   245M (does not match
> 60+60+50)
>
> (one client is a Linux netboot, and the others are using the Linux NFS
> client)
>
> But I am not an 'official', so this cannot be considered 'officially
> clarified' ;)
>
>
> > _______________________________________________
> > [hidden email] mailing list
> > http://lists.freebsd.org/mailman/listinfo/freebsd-fs
> > To unsubscribe, send any mail to "[hidden email]"
>
>


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Re: ZFS sync / ZIL clarification

Peter Maloney
On 01/30/2012 09:30 PM, Dennis Glatting wrote:

> On Mon, 2012-01-30 at 08:47 +0100, Peter Maloney wrote:
>> On 01/30/2012 05:30 AM, Mark Felder wrote:
>>> I believe I was told something misleading a few weeks ago and I'd like
>>> to have this officially clarified.
>>>
>>> NFS on ZFS is horrible unless you have sync = disabled.
>> With ESXi = true
>> with others = depends on your definition of horrible
>>
>>> I was told this was effectively disabling the ZIL, which is of course
>>> naughty. Now I stumbled upon this tonight:
>>>
>> true only for the specific dataset you specified
>> eg.
>> zfs set sync=disabled tank/esxi
>>
>>>> Just for the archives... sync=disabled won't disable disable the
>>>> zil,it'll disable waiting for a disk-flush on fsync etc.
>> Same thing... "waiting for a disk-flush" is the only time the ZIL is
>> used, from what I understand.
>>
>>>> With a batterybacked controller cache, those flushes should go to
>>>> cache, and bepretty mich free. You end up tossing away something for
>>>> nothing.
>> False I guess. Would be nice, but how do you battery back your RAM,
>> which ZFS uses as a write cache? (If you know something I don't know,
>> please share.)
>>> Is this accurate?
>> sync=disabled caused data corruption for me. So you need to have battery
>> backed cache... unfortunately, the cache we are talking about is in RAM,
>> not your IO controller. So put a UPS on there, and you are safe except
>> when you get a kernel panic (which is what happened to cause my
>> corruption). But if you get something like the Gigabyte iRAM or the
>> Acard ANS-9010
>> <http://www.acard.com.tw/english/fb01-product.jsp?prod_no=ANS-9010&type1_title=%20Solid%20State%20Drive&idno_no=270>,
>> set it as your ZIL, and leave sync=standard, you should be safer. (I
>> don't know if the iRAM works in FreeBSD, but someone
>> <http://christopher-technicalmusings.blogspot.com/2011/06/speeding-up-freebsds-nfs-on-zfs-for-esx.html>
>> told me he uses the ANS-9010)
>>
>> And NFS with ZFS is not horrible, except with ESXi's built in NFS client
>> it uses for datastores.  (the same someone that said he uses the
>> ANS-9010 also provides a 'patch' for the FreeBSD NFS server that
>> disables ESXi's stupid behavior, without disabling sync entirely, but
>> also possibly disables it for others that use it responsibly [a database
>> perhaps])
>>
>> here
>> <http://www.citi.umich.edu/projects/nfs-perf/results/cel/write-throughput.html>
>> is a fantastic study about NFS; dunno if this study resulted in patches
>> now in use or not, or how old it is [newest reference is 2002, so at
>> most 10 years old]. In my experience, the write caching in use today
>> still sucks. If I run async with sync=disabled, I can still see a huge
>> improvement (20% on large files, up to 100% for smaller files <200MB)
>> using an ESXi virtual disk (with ext4 doing write caching) compared to
>> NFS directly.
>>
>>
>> Here begins the rant about ESXi, which may be off topic:
>>
> ESXi 3.5, 4.0, 4.1, 5.0, or all of the above?
>
I didn't know 5.0.0 was available for free. Thanks for the notice.

My testing has been with 4.1.0 build 348481, but if you look around on
the net, you will find no official sensible workarounds/fixes/etc.. They
don't even acknowledge the issue is in the ESXi NFS client... even
though it is obvious. So I doubt the problem will be fixed any time
soon. Even using the "sync" option is discouraged, and they actually go
do the absolute worst thing and send O_SYNC with every write (even when
saving state of a VM; I turn off sync in zfs when I do this). Some
groups have some solutions that mitigate but do not eliminate the
problem. The issue also exists with other file systems and platforms,
but it seems the worst on ZFS. I couldn't find anything equivalent to
those solutions that work on FreeBSD and ZFS. The closest is the patch I
mentioned above
(http://christopher-technicalmusings.blogspot.com/2011/06/speeding-up-freebsds-nfs-on-zfs-for-esx.html)
which possibly would result in data corruption for non-ESXi connections
to your NFS server that responsibly use the O_SYNC flag. I didn't test
that patch, because I would rather just throw away ESXi. I hate how much
it limits you (no software raid, no file system choice, no rsync, no
firewall, top, iostat, etc.). And it handles network interruptions
terribly... in some cases you need to reboot to get it to find all the
.vmx files again. In other cases hacks work to reconnect to the NFS mounts.

But many just simply switch to iSCSI. And from what I've heard, iSCSI
also sucks on ESXi with the default settings, but a single setting fixes
most of the problem. I'm not sure if this applies to FreeBSD or ZFS
(didn't test it yet). Here are some pages from the starwind forum (where
we can assume their servers are Windows based):

Here they say "doing Write-Back Cache helps but not completely" (Windows
specific)
http://www.starwindsoftware.com/forums/starwind-f5/esxi-iscsi-initiator-write-speed-t2398-15.html

And here is something (Windows specific) about changing the ACK timing:
http://www.starwindsoftware.com/forums/starwind-f5/esxi-iscsi-initiator-write-speed-t2398.html

And here is some other page that ended up in my bookmarks:
http://www.starwindsoftware.com/forums/starwind-f5/recommended-settings-for-esx-iscsi-initiator-t2296.html

Somewhere on those 3 or linked somewhere (can't find it now), there are
instructions to turn off "Delayed ACK" (in ESXi):

in ESXi, click the host
click "Configuration" tab.
Click "Storage Adapters"
find and select the "iSCSI Software Adapter"
click "properties" (a blue link on the right, in the "details" section)
click "advanced" (must be enabled or this button is greyed out)
look for the "Delayed ACK" option in there somewhere (at the end in my
list), and uncheck the box.

And this is said to improve things considerably, but I didn't iSCSI at
all on ESXi or ZFS.

I wanted to test iSCSI on ZFS, but I found zvols to be buggy... so I
decided to avoid them. So I am not very motivated to try again.

I guess I can work around buggy zvols by using a loop device for a file
instead of a zvol... but I am always too busy. Give it a few months.

>> ESXi goes 7 MB/s with an SSD ZIL at 100% load, and 80 MB/s with a
>> ramdisk ZIL at 100% load (pathetic!),
>> something I can't reproduce (thought it was just a normal Linux client
>> with "-o sync" over 10 Gbps ethernet) got over 70MB/s with the ZIL at
>> 70-90% load,
>> and other clients set to "-o sync,noatime,..." or "-o noatime,..."with
>> the ZIL only randomly 0-5% load, but go faster than 100 MB/s. I didn't
>> test "async", and without "sync", they seem to go the same speed.
>> setting sync=disabled always goes around 100 MB/s, and changes the load
>> on the ZIL to 0%.
>>
>> The thing I can't reproduce might have been only possible on a pool that
>> I created with FreeBSD 8.2-RELEASE and then upgraded, which I no longer
>> have. Or maybe it was with "sync" without "noatime".
>>
>> I am going to test with 9000 MTU, and if it is not much faster, I am
>> giving up on NFS. My original plan was to use ESXi with a ZFS datastore
>> with a replicated backup. That works terribly using the ESXi NFS client.
>> Netbooting the OSses to bypass the ESXi client works much better, but
>> still not good enough for many servers. NFS is poorly implemented, with
>> terrible write caching on the client side. Now my plan is to use FreeBSD
>> with VirtualBox and ZFS all in one system, and send replication
>> snapshots from there. I wanted to use ESXi, but I guess I can't.
>>
>> And the worst thing about ESXi, is if you have 1 client going 7MB/s, the
>> second client has to share that 7MB/s, and non-ESXi clients will still
>> go horribly slow. If you have 10 non-ESXi clients going at 100 MB/s,
>> each one is limited to around 100 MB/s (again I only tested this with
>> 1500 MTU so far), but together they can write much more.
>>
>> Just now I tested 2 clients writing 100+100 MB/s (reported by GNU dd),
>> and 3 writing 50+60+60 MB/s (reported by GNU dd)
>> Output from "zpool iostat 5":
>> two clients:
>> tank        38.7T  4.76T      0  1.78K  25.5K   206M (matches 100+100)
>> three clients:
>> tank        38.7T  4.76T      1  2.44K   205K   245M (does not match
>> 60+60+50)
>>
>> (one client is a Linux netboot, and the others are using the Linux NFS
>> client)
>>
>> But I am not an 'official', so this cannot be considered 'officially
>> clarified' ;)
>>
>>
>>> _______________________________________________
>>> [hidden email] mailing list
>>> http://lists.freebsd.org/mailman/listinfo/freebsd-fs
>>> To unsubscribe, send any mail to "[hidden email]"
>>
>


--

--------------------------------------------
Peter Maloney
Brockmann Consult
Max-Planck-Str. 2
21502 Geesthacht
Germany
Tel: +49 4152 889 300
Fax: +49 4152 889 333
E-mail: [hidden email]
Internet: http://www.brockmann-consult.de
--------------------------------------------

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Re: ZFS sync / ZIL clarification

Dennis Glatting
On Tue, 2012-01-31 at 09:09 +0100, Peter Maloney wrote:

> On 01/30/2012 09:30 PM, Dennis Glatting wrote:
> > On Mon, 2012-01-30 at 08:47 +0100, Peter Maloney wrote:
> >> On 01/30/2012 05:30 AM, Mark Felder wrote:
> >>> I believe I was told something misleading a few weeks ago and I'd like
> >>> to have this officially clarified.
> >>>
> >>> NFS on ZFS is horrible unless you have sync = disabled.
> >> With ESXi = true
> >> with others = depends on your definition of horrible
> >>
> >>> I was told this was effectively disabling the ZIL, which is of course
> >>> naughty. Now I stumbled upon this tonight:
> >>>
> >> true only for the specific dataset you specified
> >> eg.
> >> zfs set sync=disabled tank/esxi
> >>
> >>>> Just for the archives... sync=disabled won't disable disable the
> >>>> zil,it'll disable waiting for a disk-flush on fsync etc.
> >> Same thing... "waiting for a disk-flush" is the only time the ZIL is
> >> used, from what I understand.
> >>
> >>>> With a batterybacked controller cache, those flushes should go to
> >>>> cache, and bepretty mich free. You end up tossing away something for
> >>>> nothing.
> >> False I guess. Would be nice, but how do you battery back your RAM,
> >> which ZFS uses as a write cache? (If you know something I don't know,
> >> please share.)
> >>> Is this accurate?
> >> sync=disabled caused data corruption for me. So you need to have battery
> >> backed cache... unfortunately, the cache we are talking about is in RAM,
> >> not your IO controller. So put a UPS on there, and you are safe except
> >> when you get a kernel panic (which is what happened to cause my
> >> corruption). But if you get something like the Gigabyte iRAM or the
> >> Acard ANS-9010
> >> <http://www.acard.com.tw/english/fb01-product.jsp?prod_no=ANS-9010&type1_title=%20Solid%20State%20Drive&idno_no=270>,
> >> set it as your ZIL, and leave sync=standard, you should be safer. (I
> >> don't know if the iRAM works in FreeBSD, but someone
> >> <http://christopher-technicalmusings.blogspot.com/2011/06/speeding-up-freebsds-nfs-on-zfs-for-esx.html>
> >> told me he uses the ANS-9010)
> >>
> >> And NFS with ZFS is not horrible, except with ESXi's built in NFS client
> >> it uses for datastores.  (the same someone that said he uses the
> >> ANS-9010 also provides a 'patch' for the FreeBSD NFS server that
> >> disables ESXi's stupid behavior, without disabling sync entirely, but
> >> also possibly disables it for others that use it responsibly [a database
> >> perhaps])
> >>
> >> here
> >> <http://www.citi.umich.edu/projects/nfs-perf/results/cel/write-throughput.html>
> >> is a fantastic study about NFS; dunno if this study resulted in patches
> >> now in use or not, or how old it is [newest reference is 2002, so at
> >> most 10 years old]. In my experience, the write caching in use today
> >> still sucks. If I run async with sync=disabled, I can still see a huge
> >> improvement (20% on large files, up to 100% for smaller files <200MB)
> >> using an ESXi virtual disk (with ext4 doing write caching) compared to
> >> NFS directly.
> >>
> >>
> >> Here begins the rant about ESXi, which may be off topic:
> >>
> > ESXi 3.5, 4.0, 4.1, 5.0, or all of the above?
> >
> I didn't know 5.0.0 was available for free. Thanks for the notice.
>

I downloaded ESXi 5.0 when it was free eval but since licensed it.

> My testing has been with 4.1.0 build 348481, but if you look around on
> the net, you will find no official sensible workarounds/fixes/etc.. They
> don't even acknowledge the issue is in the ESXi NFS client... even
> though it is obvious. So I doubt the problem will be fixed any time
> soon. Even using the "sync" option is discouraged, and they actually go
> do the absolute worst thing and send O_SYNC with every write (even when
> saving state of a VM; I turn off sync in zfs when I do this). Some
> groups have some solutions that mitigate but do not eliminate the
> problem. The issue also exists with other file systems and platforms,
> but it seems the worst on ZFS. I couldn't find anything equivalent to
> those solutions that work on FreeBSD and ZFS. The closest is the patch I
> mentioned above
> (http://christopher-technicalmusings.blogspot.com/2011/06/speeding-up-freebsds-nfs-on-zfs-for-esx.html)
> which possibly would result in data corruption for non-ESXi connections
> to your NFS server that responsibly use the O_SYNC flag. I didn't test
> that patch, because I would rather just throw away ESXi. I hate how much
> it limits you (no software raid, no file system choice, no rsync, no
> firewall, top, iostat, etc.). And it handles network interruptions
> terribly... in some cases you need to reboot to get it to find all the
> .vmx files again. In other cases hacks work to reconnect to the NFS mounts.
>
> But many just simply switch to iSCSI. And from what I've heard, iSCSI
> also sucks on ESXi with the default settings, but a single setting fixes
> most of the problem. I'm not sure if this applies to FreeBSD or ZFS
> (didn't test it yet). Here are some pages from the starwind forum (where
> we can assume their servers are Windows based):
>

A buddy does iSCSI by default. I can't say he ever tried NFS. He
mentioned performance questions but hadn't recent data.

My server, presently, is a PoS in need of a rebuild (it started out as
ESXi 5.0 eval but then became useful) -- obtaining disks and other
priorities are the present impediment to rebuild. I need to include
shares and I /think/ remote disks (I also want to do some analysis of
combining disparate remote disks). I've been working with big data
(<35TB) and want to assign an instance (FreeBSD) as one of my engines.
About 80% of my ESXi usage is prototyping and product eval.


> Here they say "doing Write-Back Cache helps but not completely" (Windows
> specific)
> http://www.starwindsoftware.com/forums/starwind-f5/esxi-iscsi-initiator-write-speed-t2398-15.html
>
> And here is something (Windows specific) about changing the ACK timing:
> http://www.starwindsoftware.com/forums/starwind-f5/esxi-iscsi-initiator-write-speed-t2398.html
>
> And here is some other page that ended up in my bookmarks:
> http://www.starwindsoftware.com/forums/starwind-f5/recommended-settings-for-esx-iscsi-initiator-t2296.html
>
> Somewhere on those 3 or linked somewhere (can't find it now), there are
> instructions to turn off "Delayed ACK" (in ESXi):
>
> in ESXi, click the host
> click "Configuration" tab.
> Click "Storage Adapters"
> find and select the "iSCSI Software Adapter"
> click "properties" (a blue link on the right, in the "details" section)
> click "advanced" (must be enabled or this button is greyed out)
> look for the "Delayed ACK" option in there somewhere (at the end in my
> list), and uncheck the box.
>
> And this is said to improve things considerably, but I didn't iSCSI at
> all on ESXi or ZFS.
>
> I wanted to test iSCSI on ZFS, but I found zvols to be buggy... so I
> decided to avoid them. So I am not very motivated to try again.
>
> I guess I can work around buggy zvols by using a loop device for a file
> instead of a zvol... but I am always too busy. Give it a few months.
>

When I looked into iSCSI/zvol, ZFS was 1.5 under FreeBSD and the
limitations were many. I haven't looked at 2.8.

I can't say I find ESXi the most wonderful thing in the world but if I
started to rant this text would go on for pages.

Thanks for the info.


> >> ESXi goes 7 MB/s with an SSD ZIL at 100% load, and 80 MB/s with a
> >> ramdisk ZIL at 100% load (pathetic!),
> >> something I can't reproduce (thought it was just a normal Linux client
> >> with "-o sync" over 10 Gbps ethernet) got over 70MB/s with the ZIL at
> >> 70-90% load,
> >> and other clients set to "-o sync,noatime,..." or "-o noatime,..."with
> >> the ZIL only randomly 0-5% load, but go faster than 100 MB/s. I didn't
> >> test "async", and without "sync", they seem to go the same speed.
> >> setting sync=disabled always goes around 100 MB/s, and changes the load
> >> on the ZIL to 0%.
> >>
> >> The thing I can't reproduce might have been only possible on a pool that
> >> I created with FreeBSD 8.2-RELEASE and then upgraded, which I no longer
> >> have. Or maybe it was with "sync" without "noatime".
> >>
> >> I am going to test with 9000 MTU, and if it is not much faster, I am
> >> giving up on NFS. My original plan was to use ESXi with a ZFS datastore
> >> with a replicated backup. That works terribly using the ESXi NFS client.
> >> Netbooting the OSses to bypass the ESXi client works much better, but
> >> still not good enough for many servers. NFS is poorly implemented, with
> >> terrible write caching on the client side. Now my plan is to use FreeBSD
> >> with VirtualBox and ZFS all in one system, and send replication
> >> snapshots from there. I wanted to use ESXi, but I guess I can't.
> >>
> >> And the worst thing about ESXi, is if you have 1 client going 7MB/s, the
> >> second client has to share that 7MB/s, and non-ESXi clients will still
> >> go horribly slow. If you have 10 non-ESXi clients going at 100 MB/s,
> >> each one is limited to around 100 MB/s (again I only tested this with
> >> 1500 MTU so far), but together they can write much more.
> >>
> >> Just now I tested 2 clients writing 100+100 MB/s (reported by GNU dd),
> >> and 3 writing 50+60+60 MB/s (reported by GNU dd)
> >> Output from "zpool iostat 5":
> >> two clients:
> >> tank        38.7T  4.76T      0  1.78K  25.5K   206M (matches 100+100)
> >> three clients:
> >> tank        38.7T  4.76T      1  2.44K   205K   245M (does not match
> >> 60+60+50)
> >>
> >> (one client is a Linux netboot, and the others are using the Linux NFS
> >> client)
> >>
> >> But I am not an 'official', so this cannot be considered 'officially
> >> clarified' ;)
> >>
> >>
> >>> _______________________________________________
> >>> [hidden email] mailing list
> >>> http://lists.freebsd.org/mailman/listinfo/freebsd-fs
> >>> To unsubscribe, send any mail to "[hidden email]"
> >>
> >
>
>


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Re: ZFS sync / ZIL clarification

Dennis Glatting
In reply to this post by Peter Maloney
It was pointed out off-list that my prior message was unclear and
confusing. This is my attempt at unconfusing. :)

My notation of "ZFS 2.8" is "ZFS Version 28," and "ZFS 1.5" to ZFS
Version 15.

In reference to confusion to FreeBSD versions, I run two, which is
RELENG_8 generally being migrated to RELENG_9. There are three servers
in one rack that are likely never to be upgraded and I hope to roll that
rack to permanent storage and replace it with a newer design (it would
literally be wrapped in plastic and rolled into a warehouse).

I designed (generally), built, and I am running three infrastructures.
Two of them are in the manufacturing industry and one is my personal
lab, currently at 58 cores on its way to 74 by the end of the week, if
you don't count one of the servers, various PCs and laptops, and Hyper
Threading on the Intel chips. Some of those servers are over clocked and
some liquid cooled simply because I was bored and it sounded fun. Oh,
and the spouse has banished my noisy servers to the garage (work in
progress -- cabling power, etc).





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Re: ZFS sync / ZIL clarification

Johan Hendriks-3
In reply to this post by Mark Felder-4
Mark Felder schreef:
> I believe I was told something misleading a few weeks ago and I'd like
> to have this officially clarified.
>
> NFS on ZFS is horrible unless you have sync = disabled. I was told
> this was effectively disabling the ZIL, which is of course naughty.
> Now I stumbled upon this tonight:
Well i did a test from my ESXi 5.0 server.
That server has a local store (2 x 146 GB 15k SAS drives) The ESXi
server is a HP proliant ML380 with 60 GB mem.

The ZFS server is a supermicro 3U 16 bay storage server, with a zpool
created with mirrors from all the old disk we have.
this are 80 GB drives, 250 GB drives 750 GB drives, all sata and some of
them nearly passes smartctl and one is already marked failed :D..
The machines are connected through a simple 8 port HP 1Gb switch.

If i do a copy from the local store to the NFS store, performance is
bad, well very bad.

Below is the performance graph from the esxi host. During the copy i did
the zfs set sync=disabled sanstore/ESXishare-bck  command.

http://doub.home.xs4all.nl/bench/sync.png

You see that the speed goes up, not a little, but it almost makes the
older copy graph invisable.
ESXi + ZFS without sync is disabled is a no go.

regards
Johan Hendriks

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