ZFS buggy in CURRENT? Stuck in [zio->io_cv] forever!

[Steven Hartland]

----- Original Message ----- 
From: "O. Hartmann" <ohartman at zedat.fu-berlin.de>
> 
> I have setup a RAIDZ pool comprised from 4 3TB HDDs. To maintain 4k
> block alignment, I followed the instructions given on several sites and
> I'll sketch them here for the protocol.
> 
> The operating system is 11.0-CURRENT AND 10.0-BETA2.
> 
> create a GPT partition on each drive and add one whole-covering
> partition with the option
> 
> gpart add -t freebsd-zfs -b 1M -l disk0[0-3] ada[3-6]
> 
> gnop create -S4096 gtp/disk[3-6]
> 
> Because I added a disk to an existing RAIDZ, I exported the former
> ZFS pool, then I deleted on each disk the partition and then destroyed
> the GPT scheme. The former pool had a ZIL and CACHE residing on the
> same SSD, partioned. I didn't kill or destroy the partitions on that
> SSD. To align 4k blocks, I also created on the existing gpt/log00 and
> gpt/cache00 via 
> 
> gnop create -S4096 gpt/log00|gpt/cache00
> 
> the NOP overlays.
> 
> After I created a new pool via zpool create POOL gpt/disk0[0-3].nop
> log gpt/log00.nop cache gpt/cache00.nop

You don't need any of the nop hax in 10 or 11 any more as it has
proper sector size detection. The caviate for this is when you have a
disk which adervtises 512b sectors but is 4k and we dont have a 4k
quirk in the kernel for it yet.

If you anyone comes across a case of this feel free to drop me the
details from camcontrol <identify|inquiry> <device>

If due to this you still need to use the gnop hack then you only need
to apply it to 1 device as the zpool create uses the largest ashift
from the disks.

I would then as the very first step export and import as at this point
there is much less data on the devices to scan through, not that
this should be needed but...


> I "received" a snapshot taken and sent to another storage array, after
> I the newly created pool didn't show up any signs of illness or
> corruption.
> 
> After ~10 hours of receiving the backup, I exported that pool amongst
> the backup pool, destroyed the appropriate .nop device entries via 
> 
> gnop destroy gpt/disk0[0-3]
> 
> and the same for cache and log and tried to check via 
> 
> zpool import
> 
> whether my pool (as well as the backup pool) shows up. And here the
> nasty mess starts!
> 
> The "zpool import" command issued on console is now stuck for hours and
> can not be interrupted via Ctrl-C! No pool shows up! Hitting Ctrl-T
> shows a state like
> 
> ... cmd: zpool 4317 [zio->io_cv]: 7345.34r 0.00 [...]
> 
> Looking with 
> 
> systat -vm 1
> 
> at the trhoughput of the CAM devices I realise that two of the four
> RAIDZ-comprising drives show activities, having 7000 - 8000 tps and ~
> 30 MB/s bandwidth - the other two zero!
> 
> And the pool is still inactive, the console is stuck.
> 
> Well, this made my day! At this point, I try to understand what's going
> wrong and try to recall what I did the last time different when the
> same procedure on three disks on the same hardware worked for me.
> 
> Now after 10 hours copy orgy and the need for the working array I start
> believing that using ZFS is still peppered with too many
> development-like flaws rendering it risky on FreeBSD. Colleagues
> working on SOLARIS on ZFS I consulted never saw those stuck-behaviour
> like I realise this moment.

While we only run 8.3-RELEASE currently, as we've decided to skip 9.X
and move straight to 10 once we've tested, we've found ZFS is not only
very stable but it now become critical to the way we run things.

> I don not want to repeat the procedure again. There must be a
> possibility to import the pool - even the backup pool, which is
> working, untouched by the work, should be able to import - but it
> doesn't. If I address that pool, while this crap "zpool import" command
> is still blocking the console, not willing to die even with "killall -9
> zpool", I can not import the backup pool via "zpool import BACKUP00".
> The console gets stuck immediately and for the eternity without any
> notice. Htting Ctrl-T says something like 
> 
> load: 3.59  cmd: zpool 46199 [spa_namespace_lock] 839.18r 0.00u 0.00s
> 0% 3036k
> 
> which means I can not even import the backup facility and this means
> really no fun.

I'm not sure there's enough information here to determine where any
issue may lie, but as a guess it could be that ZFS is having issues
locating the one change devices and is scanning the entire disk to
try and determine that. This would explain the IO on the one device
but not the others.

Did you per-chance have one of the disks in use for something else
and hence it may have old label information in it that wasn't cleaned
down?

    Regards
    Steve

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