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<div class="moz-cite-prefix">On 14/10/16 14:38, Dilger, Andreas
wrote:<br>
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<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:Calibri">John, with
newer Lustre clients it is possible for multiple threads to
submit non-overlapping writes concurrently (also not
conflicting within a single page), see LU-1669 for details.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:Calibri"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:Calibri">Even so,
O_DIRECT writes need to be synchronous to disk on the OSS,
as Patrick reports, because if the OSS fails before the
write is on disk there is no cached copy of the data on the
client that can be used to resend the RPC.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:Calibri"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:Calibri">The problem is
that the ZFS OSD has very long transaction commit times for
synchronous writes because it does not yet have support for
the ZIL. Using buffered writes, or having very large
O_DIRECT writes (e.g. 40MB or larger) and large RPCs (4MB,
or up to 16MB in 2.9.0) to amortize the sync overhead may be
beneficial if you really want to use O_DIRECT.
<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:Calibri"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:Calibri">Riccardo,<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:Calibri">The other
potential issue is that you have 20 OSTs on a single OSS,
which isn't going to have very good performance. Spreading
the OSTs across multiple OSS nodes is going to improve your
performance significantly when there are multiple clients
writing, as there will be N times the OSS network bandwidth,
N times the CPU, N times the RAM. It only makes sense to
have 20 OSTs/OSS if your workload is only a single client
and you want the maximum possible capacity for a given cost.</span></p>
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<br>
Hello Andreas,<br>
each OST has a separate VDEV and separate zpool.<br>
thank you<br>
<br>
<blockquote
cite="mid:28E8A029-096C-48ED-862E-EBC84702B5E1@intel.com"
type="cite">
<div class="WordSection1">
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:Calibri"><o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:Calibri"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:Calibri">Is each OST a
separate VDEV and separate zpool, or are they a single
zpool? Separate zpools have less overhead for maximum
performance, but only one VDEV per zpool means that metadata
ditto blocks are written twice per RAID-Z2 VDEV, which isn't
very efficient. Having at least 3 VDEVs per zpool is better
in this regard.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:Calibri"><o:p> </o:p></span></p>
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<div>
<div>
<p class="MsoNormal"><span
style="font-size:10.5pt;font-family:Calibri;color:black">Cheers,
Andreas<o:p></o:p></span></p>
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<div>
<p class="MsoNormal"><span
style="font-size:10.5pt;font-family:Calibri;color:black">-- <o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:10.5pt;font-family:Calibri;color:black">Andreas
Dilger<o:p></o:p></span></p>
</div>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:10.5pt;font-family:Calibri;color:black">Lustre
Principal Architect<o:p></o:p></span></p>
</div>
</div>
<p class="MsoNormal"><span
style="font-size:10.5pt;font-family:Calibri;color:black">Intel
High Performance Data Division</span><span
style="font-size:11.0pt;font-family:Calibri"><o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:Calibri"><o:p> </o:p></span></p>
<div>
<div>
<div>
<p class="MsoNormal" style="margin-left:.5in"><span
style="font-size:11.0pt;font-family:Consolas;color:black">On
2016/10/14, 15:22, "John Bauer" <<a
moz-do-not-send="true"
href="mailto:bauerj@iodoctors.com">bauerj@iodoctors.com</a>>
wrote:<o:p></o:p></span></p>
</div>
</div>
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<div>
<p class="MsoNormal" style="margin-left:.5in"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal" style="margin-left:.5in">Patrick<o:p></o:p></p>
</div>
<div id="AppleMailSignature">
<p class="MsoNormal" style="margin-left:.5in">I thought at one
time there was an inode lock held for the duration of the
direct I/O read or write. So that even if one had multiple
application threads writing direct, only one was "in flight"
at a time. Has that changed?<o:p></o:p></p>
</div>
<div id="AppleMailSignature">
<p class="MsoNormal" style="margin-left:.5in">John<br>
<br>
Sent from my iPhone<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"
style="mso-margin-top-alt:0in;margin-right:0in;margin-bottom:12.0pt;margin-left:.5in"><br>
On Oct 14, 2016, at 3:16 PM, Patrick Farrell <<a
moz-do-not-send="true" href="mailto:paf@cray.com">paf@cray.com</a>>
wrote:<o:p></o:p></p>
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<p style="margin-left:.5in"><span
style="font-family:Calibri;color:black">Sorry, I
phrased one thing wrong:<br>
I said "transferring to the network", but it's
actually until it's received confirmation the data has
been received successfully, I believe.<o:p></o:p></span></p>
<p style="margin-left:.5in"><span
style="font-family:Calibri;color:black"><o:p> </o:p></span></p>
<p style="margin-left:.5in"><span
style="font-family:Calibri;color:black">In any case,
only one I/O (per thread) can be outstanding at a time
with direct I/O.<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-left:.5in"><b><span
style="font-size:11.0pt;font-family:Calibri;color:black">From:</span></b><span
style="font-size:11.0pt;font-family:Calibri;color:black"> lustre-discuss
<<a moz-do-not-send="true"
href="mailto:lustre-discuss-bounces@lists.lustre.org">lustre-discuss-bounces@lists.lustre.org</a>>
on behalf of Patrick Farrell <<a
moz-do-not-send="true" href="mailto:paf@cray.com">paf@cray.com</a>><br>
<b>Sent:</b> Friday, October 14, 2016 3:12:22 PM<br>
<b>To:</b> Riccardo Veraldi; <a
moz-do-not-send="true"
href="mailto:lustre-discuss@lists.lustre.org">lustre-discuss@lists.lustre.org</a><br>
<b>Subject:</b> Re: [lustre-discuss] Lustre on ZFS
pooer direct I/O performance</span>
<o:p></o:p></p>
<div>
<p class="MsoNormal" style="margin-left:.5in"> <o:p></o:p></p>
</div>
</div>
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<div>
<div id="x_divtagdefaultwrapper">
<p style="margin-left:.5in"><span
style="font-family:Calibri;color:black">Riccardo,<o:p></o:p></span></p>
<p style="margin-left:.5in"><span
style="font-family:Calibri;color:black"><o:p> </o:p></span></p>
<p style="margin-left:.5in"><span
style="font-family:Calibri;color:black">While the
difference is extreme, direct I/O write
performance will always be poor. Direct I/O
writes cannot be asynchronous, since they don't
use the page cache. This means Lustre cannot
return from one write (and start the next) until
it has finished transferring the data to the
network.<o:p></o:p></span></p>
<p style="margin-left:.5in"><span
style="font-family:Calibri;color:black"><o:p> </o:p></span></p>
<p style="margin-left:.5in"><span
style="font-family:Calibri;color:black">This means
you can only have one I/O in flight at a time.
Good write performance from Lustre (or any network
filesystem) depends on keeping a lot of data in
flight at once.<o:p></o:p></span></p>
<p style="margin-left:.5in"><span
style="font-family:Calibri;color:black"><o:p> </o:p></span></p>
<p style="margin-left:.5in"><span
style="font-family:Calibri;color:black">What sort
of direct write performance were you hoping for?
It will never match that 800 MB/s from one thread
you see with buffered I/O.<o:p></o:p></span></p>
<p style="margin-left:.5in"><span
style="font-family:Calibri;color:black"><o:p> </o:p></span></p>
<p style="margin-left:.5in"><span
style="font-family:Calibri;color:black">- Patrick<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-left:.5in"><b><span
style="font-size:11.0pt;font-family:Calibri;color:black">From:</span></b><span
style="font-size:11.0pt;font-family:Calibri;color:black"> lustre-discuss
<<a moz-do-not-send="true"
href="mailto:lustre-discuss-bounces@lists.lustre.org">lustre-discuss-bounces@lists.lustre.org</a>>
on behalf of Riccardo Veraldi <<a
moz-do-not-send="true"
href="mailto:Riccardo.Veraldi@cnaf.infn.it">Riccardo.Veraldi@cnaf.infn.it</a>><br>
<b>Sent:</b> Friday, October 14, 2016 2:22:32 PM<br>
<b>To:</b> <a moz-do-not-send="true"
href="mailto:lustre-discuss@lists.lustre.org">lustre-discuss@lists.lustre.org</a><br>
<b>Subject:</b> [lustre-discuss] Lustre on ZFS
pooer direct I/O performance</span>
<o:p></o:p></p>
<div>
<p class="MsoNormal" style="margin-left:.5in"> <o:p></o:p></p>
</div>
</div>
</div>
<div>
<p class="MsoNormal" style="margin-left:.5in"><span
style="font-size:10.0pt">Hello,<br>
<br>
I would like how may I improve the situation of my
lustre cluster.<br>
<br>
I have 1 MDS and 1 OSS with 20 OST defined.<br>
<br>
Each OST is a 8x Disks RAIDZ2.<br>
<br>
A single process write performance is around
800MB/sec<br>
<br>
anyway if I force direct I/O, for example using
oflag=direct in dd, the <br>
write performance drop as low as 8MB/sec<br>
<br>
with 1MB block size. And each write it's about 120ms
latency.<br>
<br>
I used these ZFS settings<br>
<br>
options zfs zfs_prefetch_disable=1<br>
options zfs zfs_txg_history=120<br>
options zfs metaslab_debug_unload=1<br>
<br>
i am quite worried for the low performance.<br>
<br>
Any hints or suggestions that may help me to improve
the situation ?<br>
<br>
<br>
thank you<br>
<br>
<br>
Rick<br>
<br>
<br>
_______________________________________________<br>
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