Date: Fri, 1 Dec 2006 18:06:24 -0800 From: Chuck Swiger <cswiger@mac.com> To: Sean Murphy <smurphy@calarts.edu> Cc: freebsd-questions@freebsd.org Subject: Re: Soft Updates Help Message-ID: <8ED90D8B-C688-4549-85DC-8BD1B8E54690@mac.com> In-Reply-To: <4570DA18.6070505@calarts.edu> References: <4570C4D6.5030708@calarts.edu> <671FF6D7-8F30-44DF-A8ED-2456E9B80170@mac.com> <4570DA18.6070505@calarts.edu>
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On Dec 1, 2006, at 5:42 PM, Sean Murphy wrote:
> Thank you for your knowledge on this issue. I have a few
> questions that I need your help to clarify.
You are welcome, although knowledge can be a tricky thing. :-)
> "Snapshots are taken via mksnap_ffs; some other tools like fsck or
> dump also know how to create a snapshot."
>
> OK, so if I understand this correctly I do not have to
> initially take a snapshot and update this snapshot manually. The
> files system with soft updates does it correct?
If the system is rebooted with a filesystem which is marked unclean,
and if soft updates is enabled, then yes, the background fsck process
will create a snapshot automatically, and not need manual intervention.
> "Maybe. I think that softupdates is a win in almost all
> circumstances from the standpoint of data consistency, short of
> fully syncronous data & metadata updates."
>
> On this issue, if I do not have soft updates on does that
> make it a fully synchronous file system?
No. Take a look at the manpage for "mount", in particular the
section on -o which discusses async, sync, and noasync. The latter
is the default:
" noasync
Metadata I/O should be done synchronously,
while data I/O
should be done asynchronously. This is the
default."
> If the background fsck can't handle the inconsistencies it will
> report this in the /var/log/messages correct? Then is the file
> system unmounted because of the inconsistency to prevent data loss,
> so I can run a manual fsck or does it stay mounted?
It should fall back to running a foreground fsck instead, which might
indeed require manual intervention, I believe.
--
-Chuck
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