RAID gotchas!
Ferguson, Michael
ferguson at BRVMLAW.COM
Tue Jul 3 10:05:27 UTC 2007
Justin, Thanks for the offer. Please post, or send me the documentation on
how to.
'preciate it.
Ferg'
-----Original Message-----
From: fedora-list-bounces at redhat.com [mailto:fedora-list-bounces at redhat.com]
On Behalf Of Justin W
Sent: Monday, July 02, 2007 9:03 PM
To: For users of Fedora
Subject: 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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