Reoccuring ZFS performance problems
Steven Hartland
killing at multiplay.co.uk
Mon Mar 10 17:32:25 UTC 2014
Looks like you may be out of IOP/s but just incase, are you using TRIM at all?
sysctl -a |grep trim
If you are what does "gstat -d" show?
You also mention your using mysql, have you applied the standard tuning
for mysql on ZFS?
Regards
Steve
----- Original Message -----
From: "Adrian Gschwend" <ml-ktk at netlabs.org>
To: <freebsd-fs at freebsd.org>
Sent: Monday, March 10, 2014 5:05 PM
Subject: Reoccuring ZFS performance problems
> Hi group,
>
> (I have a lot of pastes in here, see http://pastebin.com/yjQnLryP for
> this email in case the mail kills too long lines)
>
> On a regular base I run into some very weird ZFS performance issues on
> my server. When it happens file IO is terribly slow and even a simple ls
> can take a long time (worst case up to minutes). Everything which relies
> on file IO is basically dead in this mode so even starting top or other
> tools is a PITA. This stage can stay from minutes to hours and goes back
> to normal after some random time. A reboot does not necessarily fix it,
> often I'm back in exactly this stage after reboot.
>
> I do not see any patterns when it happens in my monitoring (munin), in
> terms of when munin starts to time out because of it I do not see peaks
> upfront in any of the system graphs I do.
>
> When I run 'top' in this mode I see many processes in one of these states:
>
> tx->tx
> zfs
> umtxn (mainly on mysql, which is unkillable in this mode)
> uwait
>
>
> Setup:
> * FreeBSD 9.2-RELEASE-p3 in a KVM (SmartOS Solaris host, running ZFS itself)
> * I'm using mfsbsd to do a ZFS only system
> * No specific ZFS changes (I did play with some, see last part of email)
> * There are 5 jails running
> * I run various Apaches (PHP/SVN/TRAC etc), MySQL, LDAP daemon, a JVM
> and some SIP servers (Freeswitch)
> * Normal load is around 20-30% (2 cores)
> * Swap is currently on 1% usage (4G available)
> * I have 16GB of memory available, munin still shows around 1-2 GB as
> free. It can be that the issue happens faster with less memory but I
> cannot prove it either.
> * Currently no dtrace enabled so can't get much further than standard
> tools shipped with BSD
> * zpool status does not report any failures
>
> The issues are not new, they first appeared while the system was still
> running on real hardware (FBSD 8.x) and not within a KVM. Back then I
> assumed I have a hardware problem but the problem reappeared on the
> virtualized install. This install was basically a 1:1 zfs send copy plus
> some bootloader hacking of the old system so exact same software levels.
> I switched to a new install on 9.x and had the issue on every single
> release there as well. I did not try 10.x yet.
>
> fstat | wc -l:
>
> 7068
>
> (took forever to let it finish)
>
> gstat gives me:
>
> dT: 1.010s w: 1.000s
> L(q) ops/s r/s kBps ms/r w/s kBps ms/w %busy Name
> 10 575 1 0 0.2 574 653 17.8 100.4| vtbd0
> 0 0 0 0 0.0 0 0 0.0 0.0|
> PART/vtbd0/vtbd0
> 0 0 0 0 0.0 0 0 0.0 0.0| vtbd0p1
> 0 0 0 0 0.0 0 0 0.0 0.0| vtbd0p2
> 10 575 1 0 0.3 574 653 18.0 100.4| vtbd0p3
> 0 0 0 0 0.0 0 0 0.0 0.0|
> DEV/vtbd0/vtbd0
> 0 0 0 0 0.0 0 0 0.0 0.0| cd0
> 0 0 0 0 0.0 0 0 0.0 0.0|
> DEV/vtbd0p1/vtbd0p1
> 0 0 0 0 0.0 0 0 0.0 0.0|
> LABEL/vtbd0p1/vtbd0p1
> 0 0 0 0 0.0 0 0 0.0 0.0|
> gptid/e402ecce-89ca-11e2-a867-3264262b9894
> 0 0 0 0 0.0 0 0 0.0 0.0|
> DEV/vtbd0p2/vtbd0p2
> 0 0 0 0 0.0 0 0 0.0 0.0|
> LABEL/vtbd0p2/vtbd0p2
> 0 0 0 0 0.0 0 0 0.0 0.0|
> gptid/e4112d88-89ca-11e2-a867-3264262b9894
> 0 0 0 0 0.0 0 0 0.0 0.0|
> DEV/vtbd0p3/vtbd0p3
> 0 0 0 0 0.0 0 0 0.0 0.0|
> SWAP/swap/gptid/e4112d88-89ca-11e2-a867-3264262b9894
> 0 0 0 0 0.0 0 0 0.0 0.0| DEV/cd0/cd0
> 0 0 0 0 0.0 0 0 0.0 0.0|
> DEV/gptid/e402ecce-89ca-11e2-a867-3264262b9894/gptid/e402ecce-89ca
> -11e2-a867-3264262b9894
> 0 0 0 0 0.0 0 0 0.0 0.0|
> DEV/gptid/e4112d88-89ca-11e2-a867-3264262b9894/gptid/e4112d88-89ca
> -11e2-a867-3264262b9894
> 0 0 0 0 0.0 0 0 0.0 0.0|
> ZFS::VDEV/zfs::vdev/vtbd0p3
>
> ms/w changes a lot, highest I've seen right now was around 70
>
> zfs iostat 2:
>
> capacity operations bandwidth
> pool alloc free read write read write
> ---------- ----- ----- ----- ----- ----- -----
> tank 173G 21.5G 3 56 30.9K 535K
> tank 173G 21.5G 62 376 49.0K 1.22M
> tank 173G 21.5G 46 340 84.3K 565K
> tank 173G 21.5G 45 566 74.6K 800K
> tank 173G 21.5G 32 222 92.0K 958K
> tank 173G 21.5G 63 392 120K 1.10M
> tank 173G 21.5G 16 286 14.2K 338K
> tank 173G 21.5G 29 313 24.6K 831K
> tank 173G 21.5G 0 289 0 445K
> tank 173G 21.5G 27 244 32.6K 293K
> tank 173G 21.5G 43 385 42.8K 477K
> tank 173G 21.5G 31 329 15.7K 710K
> tank 173G 21.5G 65 394 46.8K 1.50M
> tank 173G 21.5G 80 320 127K 754K
> tank 173G 21.5G 30 425 144K 1.09M
> tank 173G 21.5G 13 399 25.9K 379K
> tank 173G 21.5G 10 194 5.22K 162K
> tank 173G 21.5G 18 311 45.5K 1.02M
> tank 173G 21.5G 29 202 58.5K 344K
> tank 173G 21.5G 32 375 108K 926K
>
>
> on the host OS (SmartOS) zpool iostat 2 shows me (there is one other
> FBSD box but there is almost no IO on this one):
>
> capacity operations bandwidth
> pool alloc free read write read write
> ---------- ----- ----- ----- ----- ----- -----
> zones 602G 230G 5 278 44.0K 2.42M
> zones 602G 230G 2 154 19.9K 2.18M
> zones 602G 230G 0 1.47K 0 10.3M
> zones 602G 230G 0 128 0 1.44M
> zones 602G 230G 0 270 0 2.61M
> zones 602G 230G 0 1.39K 0 10.2M
> zones 602G 230G 0 114 7.96K 2.10M
> zones 602G 230G 0 979 7.96K 7.84M
>
> When the guest system is not in this state the writes are lower and I
> don't see modes where I have 0 on reads.
>
> I was googling around about this topic forever and I do find people who
> report similar issues. No one I've contacted found a real explanation
> for it. Based on various guides I started adapting the basic config:
>
> cat /boot/loader.conf:
>
> vfs.zfs.zfetch.block_cap=64
>
> # this one was horrible, bootup alone was dogslow
> #vfs.zfs.write_limit_override=1048576
>
> #vfs.zfs.txg.timeout="5"
>
> # so far good results?
> vfs.zfs.prefetch_disable="1"
>
> First I thought disabling prefetch did solve the issue for a while. But
> it looks like I was too optimistic with that one. However, ls feels
> *much* faster when the system is happy since I disabled prefetch.
>
> I'm really totally lost on this one so I would appreciate hints about
> how to debug that.
>
> I'm willing to test whatever it takes to figure out where this issue is.
>
> thanks
>
> Adrian
>
>
>
>
>
>
>
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