Re: RAID gotchas!

Roberto Ragusa wrote:
Jeffrey Ross wrote:
Roberto Ragusa wrote:
Dump is considered a bad choice by Linus himself; read this:

http://lwn.net/2001/0503/a/lt-dump.php3

(a few years ago, but the words are quite strong)

Best regards.
I've read the arguments here's the rebuttal to the 2001 message:
http://dump.sourceforge.net/isdumpdeprecated.html

Thank you for this link, very interesting.
Basically thay say that there was a bug in 2.4, now fixed.

They claim three advantages when using dump, but they are rather
weak, I have to say (IMHO).

1) dump unmounted filesystem; but why not just mount it read-only
and use a normal file copy tool? they talk about trying to dump
corrupted unmountable filesystems for rescue purposes, but it looks
like a very stretched motivation, especially when trying to prove
that dump is preferable for normal uncorrupted filesystems.

For less informed readers (or curious readers later finding this thread in a search of the archives), copying unmountable file systems is already possible: use dd. You can even take the image of a partition (or a whole drive) and mount the file system located within it using loop devices (though the whole drive takes more work aligning the mount to the beginning of a "partition", and thus, an understandable file system).

[snip]

6) dump can not create accessible backups; I want to be able
to use the files in my backup (find, grep,...), not just
restore them.

Using the method I describe above, this is possible.

Finally they say that by using snapshots you can have a stable
read-only image of the filesystem to run dump on. But the same
is true for other tools too.

I just backed up my server using a combination of an LVM snapshot, dd to copy the partition initially, and now it'll be maintained with nightly rsyncs to a mounted image file. (Note: If anyone is interested, I can post some documentation describing how I set up the backup and the script which will keep my backup up-to-date).

Certainly there is not a right way and wrong way to do things.
If dump gives you reliable backups and you are used to it,
it's a valid choice.

File copy tools will remain my preferred choice.
In this exact moment I have two backups running across the
LAN; they involve a couple of millions of files; one is
using tar|tar, another rsync. (I'm not kidding)
All filesystems are reiser here, so I couldn't try dump if I
wanted, but even if I could, I think I would not. :-)

You gave me an opportunity to understand dump better.
For what I've seen, it should be called e2dump and
should be part of ext2progs, together with e2fsck,
e2label, resize2fs and dumpe2fs (which is something else).
It is a filesystem tool, not a file tool.
Linux is not always ext2/ext3.

Maybe the summary of all this is just that dump is a
tool to backup a filesystem, but I want to backup the files.

Best regards.

Justin W

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