comment on retries below...
Paul Boven wrote:
> Hi Eric, everyone,
>
> Eric Schrock wrote:
>> There have been many improvements in proactively detecting failure,
>> culminating in build 77 of Nevada. Earlier builds:
>>
>> - Were unable to distinguish device removal from devices misbehaving,
>> depending on the driver and hardware.
>>
>> - Did not diagnose a series of I/O failures as disk failure.
>>
>> - Allowed several (painful) SCSI retries and continued to queue up I/O,
>> even if the disk was fatally damaged.
>
>> Most classes of hardware would behave reasonably well on device removal,
>> but certain classes caused cascading failures in ZFS, all which should
>> be resolved in build 77 or later.
>
> I seem to be having exactly the problems you are describing (see my
> postings with the subject 'zfs on a raid box'). So I would very much
> like to give b77 a try. I'm currently running b76, as that's the latest
> sxce that's available. Are the sources to anything beyond b76 already
> available? Would I need to build it, or bfu?
>
> I'm seeing zfs not making use of available hot-spares when I pull a
> disk, long and indeed painful SCSI retries and very poor write
> performance on a degraded zpool - I hope to be able to test if b77 fares
> any better with this.
The SCSI retries are implemented at the driver level (usually sd) below
ZFS. By default, the timeout (60s) and retry (3 or 5) counters are
somewhat conservative and intended to apply to a wide variety of hardware,
including slow CD-ROMs and ancient processors. Depending on your
situation and business requirements, these may be tuned. There is a
pretty good article on BigAdmin which describes tuning the FC side of
the equation (ssd driver).
http://www.sun.com/bigadmin/features/hub_articles/tuning_sfs.jsp
Beware, making these tunables too small can lead to an unstable system.
The article does a good job of explaining how interdependent the tunables
are, so hopefully you can make wise choices.
-- richard
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