Date: Mon, 7 Mar 2022 12:55:06 -0500 From: Karl Denninger <karl@denninger.net> To: freebsd-fs@freebsd.org Subject: Re: md disks EXTREMELY slow 12.3-STABLE Message-ID: <fc9b4816-6da1-04dd-0806-21d539c88233@denninger.net> In-Reply-To: <bdc83a45-4bed-d896-0709-e8253bded1bb@sentex.net> References: <97013161-b119-4c98-a294-c733ca000a34@denninger.net> <e775b9ba-d506-8189-ab18-c8bc4f384c42@gmx.at> <8eb0baaa-f22b-57f7-6b6f-6d93ddb2dee5@denninger.net> <bdc83a45-4bed-d896-0709-e8253bded1bb@sentex.net>
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On 3/4/2022 20:11, mike tancsa wrote:
> On 3/4/2022 3:06 PM, Karl Denninger wrote:
>> On 3/4/2022 14:34, infoomatic wrote:
>>> On 04.03.22 17:22, Karl Denninger wrote:
>>>> Load average is 0.3 yet the md0 drive is pinned at 100% busy with just
>>>> 50 transactions-per-second!
>>>
>>> you mean md(4), the memory disk, right? ... just to be sure it is no
>>> typo
>>>
>> Correct.
>>
>> I think I've found the issue -- The "-13" build is using a vnode on
>> the spinning rust ZFS pool (albeit a fairly high-performance one
>> comprised of mirrored vdevs) for backing store. I'm not sure WHY
>> this winds up being so insanely slow, but it does. I'm going to move
>> it either to memory/swap (since I have a bunch) or stick it on the
>> SSD pool since creating an md in RAM is, as expected, ridiculously fast.
>>
>
> /Try doing mount -o async. It makes a big difference speed wise for
> writes.
> /
>
> / ---Mike/
>
Mounting the md filesystem -async does not help at all.
/dev/md0s1 on /work/Crochet-work-ARM64-14/_.mount.boot (msdosfs, local)
/dev/md0s2a on /work/Crochet-work-ARM64-14/_.mount.freebsd (ufs,
asynchronous, local)
It appears the interaction between using a ZFS-hosted vnode as backing
store for an md() on spinning media results in some sort of pathological
behavior. "make installworld", which is simply file copies, demonstrates
the problem.
Putting the backing store on a ZFS pool that is SSD-based results in
expected performance. I thus surmise that the issue is that the
interrelationship between the two is leading to a crazy amount of seek
activity on the devices in question. The zfs filesystem in question
(/work) has the default record size (128K) and lz4 compression enabled,
nothing else interesting.
--
Karl Denninger
karl@denninger.net
/The Market Ticker/
/[S/MIME encrypted email preferred]/
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<div class="moz-cite-prefix">On 3/4/2022 20:11, mike tancsa wrote:<br>
</div>
<blockquote type="cite"
cite="mid:bdc83a45-4bed-d896-0709-e8253bded1bb@sentex.net">On
3/4/2022 3:06 PM, Karl Denninger wrote:
<br>
<blockquote type="cite">On 3/4/2022 14:34, infoomatic wrote:
<br>
<blockquote type="cite">On 04.03.22 17:22, Karl Denninger wrote:
<br>
<blockquote type="cite">Load average is 0.3 yet the md0 drive
is pinned at 100% busy with just
<br>
50 transactions-per-second!
<br>
</blockquote>
<br>
you mean md(4), the memory disk, right? ... just to be sure it
is no typo
<br>
<br>
</blockquote>
Correct.
<br>
<br>
I think I've found the issue -- The "-13" build is using a vnode
on the spinning rust ZFS pool (albeit a fairly high-performance
one comprised of mirrored vdevs) for backing store. I'm not
sure WHY this winds up being so insanely slow, but it does. I'm
going to move it either to memory/swap (since I have a bunch) or
stick it on the SSD pool since creating an md in RAM is, as
expected, ridiculously fast.
<br>
<br>
</blockquote>
<br>
/Try doing mount -o async. It makes a big difference speed wise
for writes.
<br>
/
<br>
<br>
/ ---Mike/
<br>
<br>
</blockquote>
<p>Mounting the md filesystem -async does not help at all.</p>
<p>/dev/md0s1 on /work/Crochet-work-ARM64-14/_.mount.boot (msdosfs,
local)<br>
/dev/md0s2a on /work/Crochet-work-ARM64-14/_.mount.freebsd (ufs,
asynchronous, local)<br>
</p>
<p>It appears the interaction between using a ZFS-hosted vnode as
backing store for an md() on spinning media results in some sort
of pathological behavior. "make installworld", which is simply
file copies, demonstrates the problem.<br>
</p>
<p>Putting the backing store on a ZFS pool that is SSD-based results
in expected performance. I thus surmise that the issue is that
the interrelationship between the two is leading to a crazy amount
of seek activity on the devices in question. The zfs filesystem
in question (/work) has the default record size (128K) and lz4
compression enabled, nothing else interesting.</p>
<div class="moz-signature">-- <br>
Karl Denninger<br>
<a href="mailto:karl@denninger.net" class="moz-txt-link-freetext">karl@denninger.net</a><br>
<i>The Market Ticker</i><br>
<font size="-2"><i>[S/MIME encrypted email preferred]</i></font></div>
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