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Re: [PATCH] xfsdump: use the full 32-bit generation number

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Subject: Re: [PATCH] xfsdump: use the full 32-bit generation number
From: Bill Kendall <wkendall@xxxxxxx>
Date: Mon, 06 Feb 2012 11:40:09 -0600
Cc: xfs@xxxxxxxxxxx
In-reply-to: <20120205133648.GA27225@xxxxxxxxxxxxx>
References: <1325880565-20934-1-git-send-email-wkendall@xxxxxxx> <20120205133648.GA27225@xxxxxxxxxxxxx>
User-agent: Thunderbird 1.5.0.14ubu (X11/20080502)
Christoph Hellwig wrote:
On Fri, Jan 06, 2012 at 02:09:25PM -0600, Bill Kendall wrote:
dump format version has been bumped to 3. xfsdump also required changes to
its inode-to-generation cache. This map is not persistent though, so no
compatibility or version changes were required there.

Shouldn't the be an option to still generate the old format for
compatibility reasons?

The new format contains more information than the old. The new
xfsrestore can drop back to using 12-bit generation numbers even
if the dump used 32 bits. It will do this automatically when
applying a series of restores if the oldest dump used only 12 bits.

It's possible that a site would revert to an old xfsdump in the
middle of a series of incremental backups, allowing for the oldest
backup to use 32-bit generation numbers and a newer backup to use
only 12 bits. xfsrestore won't get this right, so a case could be
made for having a "force 12-bit generation numbers" option on
xfsrestore.

You were referring to an xfsdump option. What use case did you
have in mind? Compatibility with an old restore?

Thanks,
Bill

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