Scott Laird wrote:
> On 10/18/07, Neil Perrin <[EMAIL PROTECTED]> wrote:
>>> So, the only way to lose transactions would be a crash or power loss,
>>> leaving outstanding transactions in the log, followed by the log
>>> device failing to start up on reboot? I assume that that would that
>>> be handled relatively cleanly (files have out of data data), as
>>> opposed to something nasty like the pool fails to start up.
>> I just checked on the behaviour of this. The log is treated as part
>> of the main pool. If it is not replicated and disappears then the pool
>> can't be opened - just like any unreplicated device in the main pool.
>> If the slog is found but can't be opened or is corrupted then then the
>> pool will be opened but the slog isn't used.
>> This seems a bit inconsistent.
>
> Hmm, yeah. What would happen if I mirrored the ramdisk with a hard
> drive? Would ZFS block until the data's stable on both devices, or
> would it continue once the write is complete on the ramdisk?
ZFS ensures all mirror sides have the data before returning.
>
> Failing that, would replacing the missing log with a blank device let
> me bring the pool back up, or would it be dead at that point?
Replacing the device would work:
: mull ; mkfile 100m /p1 /p2
: mull ; zpool create whirl /p1 log /p2
: mull ; echo abc > /whirl/f
: mull ; sync
: mull ; rm /p2
: mull ; sync
<reset system>
: mull ; zpool status
pool: whirl
state: UNAVAIL
status: One or more devices could not be opened. There are insufficient
replicas for the pool to continue functioning.
action: Attach the missing device and online it using 'zpool online'.
see: http://www.sun.com/msg/ZFS-8000-3C
scrub: none requested
config:
NAME STATE READ WRITE CKSUM
whirl UNAVAIL 0 0 0 insufficient replicas
/p1 ONLINE 0 0 0
logs UNAVAIL 0 0 0 insufficient replicas
/p2 UNAVAIL 0 0 0 cannot open
: mull ; mkfile 100m /p2 /p3
: mull ; zpool online whirl /p2
warning: device '/p2' onlined, but remains in faulted state
use 'zpool replace' to replace devices that are no longer present
: mull ; zpool status
pool: whirl
state: ONLINE
status: One or more devices could not be used because the label is missing or
invalid. Sufficient replicas exist for the pool to continue
functioning in a degraded state.
action: Replace the device using 'zpool replace'.
see: http://www.sun.com/msg/ZFS-8000-4J
scrub: none requested
config:
NAME STATE READ WRITE CKSUM
whirl ONLINE 0 0 0
/p1 ONLINE 0 0 0
logs ONLINE 0 0 0
/p2 UNAVAIL 0 0 0 corrupted data
errors: No known data errors
: mull ; zpool replace whirl /p2 /p3
: mull ; zpool status
pool: whirl
state: ONLINE
scrub: resilver completed with 0 errors on Thu Oct 18 18:16:39 2007
config:
NAME STATE READ WRITE CKSUM
whirl ONLINE 0 0 0
/p1 ONLINE 0 0 0
logs ONLINE 0 0 0
replacing ONLINE 0 0 0
/p2 UNAVAIL 0 0 0 corrupted data
/p3 ONLINE 0 0 0
errors: No known data errors
: mull ; zpool status
pool: whirl
state: ONLINE
scrub: resilver completed with 0 errors on Thu Oct 18 18:16:39 2007
config:
NAME STATE READ WRITE CKSUM
whirl ONLINE 0 0 0
/p1 ONLINE 0 0 0
logs ONLINE 0 0 0
/p3 ONLINE 0 0 0
errors: No known data errors
: mull ; zfs mount
: mull ; zfs mount -a
: mull ; cat /whirl/f
abc
: mull ;
>
>>>>> 3. What about corruption in the log? Is it checksummed like the rest of
>>>>> ZFS?
>>>> Yes it's checksummed, but the checksumming is a bit different
>>>> from the pool blocks in the uberblock tree.
>>>>
>>>> See also:
>>>> http://blogs.sun.com/perrin/entry/slog_blog_or_blogging_on
>>> That started this whole mess :-). I'd like to try out using one of
>>> the Gigabyte SATA ramdisk cards that are discussed in the comments.
>> A while ago there was a comment on this alias that these cards
>> weren't purchasable. Unfortunately, I don't know what is available.
>
> The umem one is unavailable, but the Gigabyte model is easy to find.
> I had Amazon overnight one to me, it's probably sitting at home right
> now.
Cool let us know how it goes.
Neil.
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