Access to UFS stuck during snapshot.

[Eric Anderson]

Kris Kennaway wrote:
> On Wed, May 24, 2006 at 02:17:51PM +0800, Kent Ho wrote:
>> Hi,
>>
>> I having problems accessing file system during snapshot runs.  snapshot 
>> takes approximately 10 to 20 mins to run.
>>
>> During that time access to files in the file system are blocked until 
>> the snapshot has completed.  Lot of processes was stuck and piles up on 
>> the fs.
>>
>> This fs stores mailboxes and it's accessed 24/7.  This is similar to 
>> what described in this thread.
>>
>> http://www.freebsd.org/cgi/getmsg.cgi?fetch=14968+0+/usr/local/www/db/text/2006/freebsd-fs/20060312.freebsd-fs
>>
>> Has this been improved or fixed in recent releases, I see a bunch of 
>> fixes in march?  any possible work around?  any alternatives or 
>> recommendations?  Looking for high availability fs with snapshots.
> 
> It's by design.
> 
> Kris

I found that making the .snap directories permissions 0700, and then 
making a subdirectory under the .snap that stores the actual snapshots 
helped, as long as I did not make any stat() calls to the snapshot file 
that was in snaplk state.

Kris - you've had your head deep in the snapshot spaghetti recently - is 
this blocking just a matter of the locking on the snapshot file and a 
stat() call blocking on it, which causes an upward locking to the root 
dir of the filesystem?  Could this be avoided by 'hiding' the snapshot 
file while a snapshot is in progress?  I have been tinkering with hiding 
the snapshot directory during snapshot creation, but I don't have any 
results of anything yet, still too early.  I'm a wannabe hacker, so my 
progress is slow.


Eric





-- 
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Eric Anderson        Sr. Systems Administrator        Centaur Technology
Anything that works is better than anything that doesn't.
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