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Date:      Sun, 20 Jul 2014 23:49:55 -0400
From:      Nikolai Lifanov <lifanov@mail.lifanov.com>
To:        Steven Hartland <killing@multiplay.co.uk>
Cc:        svn-src-head@freebsd.org, src-committers@freebsd.org, Xin LI <delphij@freebsd.org>
Subject:   Re: svn commit: r268855 - in head: cddl/contrib/opensolaris/cmd/ztest sys/cddl/contrib/opensolaris/uts/common/fs/zfs sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys
Message-ID:  <1048c8cc25685b1216b0f1714c4494f1@mail.lifanov.com>
In-Reply-To: <09AF6051EC3848B6B691A5570B5B065E@multiplay.co.uk>
References:  <201407182041.s6IKffMR077972@svn.freebsd.org> <5d0810f5950150ef60044acf239adb4a@mail.lifanov.com> <09AF6051EC3848B6B691A5570B5B065E@multiplay.co.uk>

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On 2014-07-20 22:56, Steven Hartland wrote:
> ----- Original Message ----- From: "Nikolai Lifanov" 
> <lifanov@mail.lifanov.com>
> To: "Xin LI" <delphij@freebsd.org>
> Cc: <src-committers@freebsd.org>; <svn-src-head@freebsd.org>
> Sent: Monday, July 21, 2014 2:22 AM
> Subject: Re: svn commit: r268855 - in head:
> cddl/contrib/opensolaris/cmd/ztest
> sys/cddl/contrib/opensolaris/uts/common/fs/zfs
> sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys
> 
> 
>> On 2014-07-18 16:41, Xin LI wrote:
>>> Author: delphij
>>> Date: Fri Jul 18 20:41:40 2014
>>> New Revision: 268855
>>> URL: http://svnweb.freebsd.org/changeset/base/268855
>>> 
>>> Log:
>>>   MFV r268848:
>>> 
>>>   Instead of asserting all zio's be properly aligned, only assert
>>>   on the logical ones.
>>> 
>>>   Cap uberblocks at 8k, otherwise with ashift=17, there would be
>>>   only one uberblock.
>>> 
>>>   This fixes a problem that zdb would trip assert on pools with
>>>   ashift >= 0xe (8k).
>>> 
>>>   While there, also change the code so it only attempt to condense
>>>   space map unless the uncondensed size consumes greater than
>>>   zfs_metaslab_condense_block_threshold blocks.
>>> 
>>>   Illumos issue:
>>>     4958 zdb trips assert on pools with ashift >= 0xe
>>> 
>>>   MFC after: 2 weeks
>>> 
>> 
>> This specific commit makes boot hang just before mounting the root 
>> dataset for me when vfs.zfs.vdev.cache.size tunable is set. Unsetting 
>> this tunable or reverting this commit (currently running r268933 minus 
>> r268855) fixes the boot for me.
>> 
>> Please let me know if I can provide any more information.
> 
> Interesting, is there a reason you enabled vdev caching as its been
> disabled by default for quite some time with the comment:
> 
> * TODO: Note that with the current ZFS code, it turns out that the
> * vdev cache is not helpful, and in some cases actually harmful.  It
> * is better if we disable this.  Once some time has passed, we should
> * actually remove this to simplify the code.  For now we just disable
> * it by setting the zfs_vdev_cache_size to zero.  Note that Solaris 11
> * has made these same changes.
> 
>    Regards
>    Steve
> 
> _______________________________________________
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I noticed that it was disabled on default and I'm not seeing any ill 
effect now that I have it disabled. I don't find vdev cache beneficial, 
but I had it in my loader.conf for some time, and I had to remove it to 
get the system to boot. If it's going to be broken going forward, 
perhaps it's worthwhile to just remove the tunable?

- Nikolai Lifanov



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