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Re: file system dumps

On 22:10 30 Jan 2003, Michael Weiner <hunter userfriendly net> wrote:
| On Thu, 2003-01-30 at 21:27, Cameron Simpson wrote:
| My apologies for being nebulous, i was looking for a tool "like"
| xfsdump. Honestly, it hadnt occored to me to investigate dump.I am more
| accustomed to doing a dd if=/dev/sda of=/dev/sdb bs=10 & but seems
| somewhat inefficient to me as it takes about 3 hours to complete.

Unless you filesystem quite full it's wasting a lot of time copying
empty space. But it will at least be doing sequential access - tar will
be scattered over the disc depending on the file block layout; probably
mostly-sequential within a given file.

| But i
| will say, does make a nice "seed" mirror, but same issue applies - if
| the source is bad, the target will be bad.

More to the point, the image can be corrupt; tar or rsync (or anything
above the filesystem layer) can get a file during modification, but below
that you can end up with a busted filesystem - needing fsck - very bad.

Gordon Messmer's remark about xfs's snapshot facility is right on - if
you want "dump" of a live filesystem it may be worth your while using
XFS for such things.

| But lets assume the source
| AND target are both good going in. I was planning on just going ahead
| and trying your tar or dd.

I would prefer tar myself. Above the filesystem layer.

| THANK YOU thats exactly what i was looking
| for, as for the tar command sequence. And now, that we have an exact
| duplicate, using rsync, disk-to-disk, how are you using rsync to keep
| them in sync?

Just run it again:

	rsync -avWHP source/. target/.

Drop the "v" and "P" when happy. The "W" says copy-whole-file - when the
source and target are on the same machine it's better to just throw the
whole file across instead of using the checksum partial update stuff.

Cameron Simpson, DoD#743        cs zip com au    http://www.zip.com.au/~cs/

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