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Date:      Wed, 05 Oct 2011 17:52:18 -0400
From:      Daniel Staal <DStaal@usa.net>
To:        Dave Cundiff <syshackmin@gmail.com>, questions@freebsd.org
Subject:   Re: ZFS Write Lockup
Message-ID:  <EB6EF2AF144081215CE275CC@mac-pro.magehandbook.com>
In-Reply-To: <CAKHEz2a+RFmcCyEMnooDmb8vERA-qg0A474LZ9mLtPvoij8Xmw@mail.gmail.com>
References:  <CAKHEz2a+RFmcCyEMnooDmb8vERA-qg0A474LZ9mLtPvoij8Xmw@mail.gmail.com>

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--As of October 4, 2011 2:43:45 AM -0400, Dave Cundiff is alleged to have 
said:

> I don't know what triggers the problem but I know how to fix it. If I
> perform a couple snapshot deletes the IO will come back in line every
> single time. Fortunately I have LOTS of snapshots to delete.
>
> [root@san2 ~]# zfs list -r -t snapshot | wc -l
>     5236
> [root@san2 ~]# zfs list -r -t volume | wc -l
>       17

--As for the rest, it is mine.

I have no good advice, but I have a thought.  ;)

The thought is: Why so many snapshots?  And: How many other people have 
that many snapshots?  I know that ZFS is supposed to be able to handle huge 
numbers of snapshots (far more than a few thousand, from my understanding), 
but if it hasn't been used much in that config, there may be bugs lurking.

You might try weeding through and figuring out if you can drop a good 
amount of those snapshots.  Also, try the filesystems list.  They may have 
better thoughts.

Daniel T. Staal

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