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List:       linux-dump-users
Subject:    Re: [Dump-users] Dump on live filesystem
From:       Stelian Pop <stelian () popies ! net>
Date:       2003-09-13 20:07:13
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On Wed, Sep 10, 2003 at 04:20:35PM +0200, Vladislav Kurz wrote:

> Hi all,
> 
> I read thoroughly the article "Is dump deprecated?" and related discussion. 
> From all that I concluded that dumping unmounted or read-only filesystem is 
> safe, but dumping live filesystem is like a lottery. If the filesystem is 
> idle it should be OK but if some write happens in the meantime I might lose.
> 
> I want to ask if mounting the filesystem with sync option can eliminate (or 
> reduce) the risk of dumping garbage or not. I dont mind having the system 
> slowed down during the dump, but I don't wont my daemons crashed because they 
> can't write to spool, log, etc when I remount read-only.
> 
> So what I want to do is this:
> 
> # mount -o remount,sync /dev/hda1
> # dump .... /dev/hda1
> # mount -o remount,async /dev/hda1
> 
> I'm looking forward to your opnions.

From what I understand, mounting a filesystem with the 'sync' option
will cause any file system related syscall to be synchronous, meaning
that the syscall will return only when the data have been effectively
flushed to the disk.

This doesn't change the fact that dump can still access the underlying
data while it is being written (when the syscalls are being executed).

Flushing more often will make the disk be consistent much more often 
than without 'sync', but it will not eliminate entirely the problem.

Stelian.
-- 
Stelian Pop <stelian@popies.net>


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