From owner-freebsd-fs@FreeBSD.ORG  Wed Jan  9 03:18:34 2013
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Date: Wed, 9 Jan 2013 03:18:34 +0000
From: John <jwd@FreeBSD.org>
To: Hiroki Sato <hrs@FreeBSD.org>
Subject: Re: rc.d script for memory based zfs intent log
Message-ID: <20130109031834.GA14386@FreeBSD.org>
References: <20130109023327.GA1888@FreeBSD.org>
 <20130109.115240.1198411557684741197.hrs@allbsd.org>
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----- Hiroki Sato's Original Message -----
> John <jwd@freebsd.org> wrote
>   in <20130109023327.GA1888@FreeBSD.org>:
> 
> jw> Hi Folks,
> jw>
> jw>    Here's an rc.d script that provides a nice performance boost on
> jw> ZFS/NFS based file servers. It also helps in other areas not specific
> jw> to NFS.
> jw>
> jw>    It attaches the log device at system startup and removes it at
> jw> system shutdown time. Example;
> jw>
> jw> memzil_pools="tank"
> jw> memzil_bootfs="YES"
> jw> service memzil onestart
> jw> zpool status tank
> jw> service memzil onestop
> jw>
> jw>    This configuration provides a nice performance boost especially to
> jw> NFS, but also helps in other areas not specific to NFS.
> jw>
> jw>    Please DO NOT USE this script if your system is not UPS backed, preferably
> jw> with dual power supplies on separate circuits. If your system crashes you
> jw> may lose data. The script contains information on recovery.
> jw>
> jw> http://people.freebsd.org/~jwd/memzil.txt
> jw>
> jw>    Comments/Improvements appreciated.
> 
>  Why is simply setting sync=disabled to the ZFS dataset not enough?

As you refer to, my understanding is that sync=disabled is at the dataset
layer. The zil approach is at the zpool layer - sync=disabled would be
nice at the zpool layer. 

-John

> -- Hiroki