sugoll (sugoll) wrote,

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Linux backups

I really don't see why this should be so damn painful.

Back here, there's some discussion about using dd, which is what I'm attempting to do now, but it's never satisfactory.

For starters, it's taken me a long time just to get an external disk that mounts reliably. I dunno why, but when I plug it in, I get permissions errors when the auto-mount happens - most of the time. Previously, it was FAT-formatted, and mounted okay, but would generally be read-only - most of the time. Now it's ext3-formatted, and fails to auto-mount, but an explicit mount as root works.

So, I'm dd'ing onto that. dd'ing just the main partition doesn't seem to produce something I can loop-back mount afterwards, and if I can't loop-mount it, I can't verify it contains anything useful.

(I could just dd directly over the external disk, I suppose; I don't know whether the disks' geometries have to match, and I'm pretty sure they don't).

Reading around, there are a few pages that advise dd'ing the whole disk, rather than the partition, so that's what I'm trying at the moment:
dd if=/dev/hda of=backup.img

(not all of them recommend this; some of them recommend all sorts of different approaches, and some of them were incredibly long-winded.)

Problem is, I've done this a number of times, mostly they terminate with:

dd: reading `/dev/hda': Input/output error

You don't want to see errors, when creating backups. You want to see "everything copied perfectly."

At least one of the pages I've seen suggests using dd options to keep going when read errors occur, which doesn't boost my confidence much either.

And all of the .img files created are of different sizes. Um, shouldn't they be constant sizes?

The mounting is painful; seems I need to use fdisk -l to determine the offsets into the img of the various partitions, then use:
mount -r -o loop,offset=$off -t ext3 $img /mnt/x

where $off is the start of the partition I want. This has worked at least once, but not reliably.

What I want to know is: why is this so painful? Back in the day, everyone used tape drives, and they all used dump and restore, which were pretty standard stuff: level 0, plus incremental backups.  So why doesn't yer average Linux installation come with something that has a much simpler interface? Copy all data from here to there. Show me it's worked, so that I can browse it. Copy it back.
Tags: backups, computers, linux
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