Re: How do folk back these up?

You're right that RAID is not the same as a backup, it just provides protection against data loss due to built-in redundancy.

In some advanced file system like Sun's ZFS or NetApp's offerings, there *is* protection against data being unintentionally corrupted or deleted by the user, application or OS: they are called snapshots. Files and directories referenced by snapshots cannot be deleted until the referring snapshot is deleted -- so there is your protection against loss. Also files/dirs referenced by snapshots cannot be modified -- these file systems employ a method called 'copy-on-write' which means that if a file referenced by a snapshot is modified, the file system creates a copy. If I remember correctly, the common blocks of the two files are not duplicated, to save space, but don't quote me on that :)

A traditional 2-drive mirror is fine until you need, in this case, 2.1 TB. Also traditional mirrors often don't repair files that can't be read -- the file system/RAID controller often just returns the data on the good half of the mirror. However, ZFS also repairs the faulty file on the bad side of the mirror, as indeed it does in any redundant setup: mirror, RAID-Z1 (like RAID 5), or RAID-Z2 (like RAID 6).

For backup/syncing of files that you mention, again, ZFS offers a way of doing this -- with one important difference and huge benefit: you will never lose any data that gets deleted if you use (1) automatic snapshotting (via cron every 30 minutes or whatever), and (2) use 'zfs send/receive' to send an initial full backup and subsequent incremental backups, in which ZFS detects diffs between snapshots and sends only the differences, to another storage pool, which might be on the same machine or a different machine on the LAN/WAN.

These links might be of further interest:

http://breden.org.uk/2008/05/12/home-fileserver-zfs-snapshots/

http://breden.org.uk/2008/05/12/home-fileserver-backups-from-zfs-snapshots/

http://blogs.sun.com/erwann/date/20081013

http://opensolaris.org/os/community/zfs/docs/zfs_last.pdf

http://blogs.sun.com/timf/en_IE/entry/zfs_automatic_snapshots_0_11

http://channelsun.sun.com/video/opensolaris+demo+time+slider+in+opensolaris+2008.11/2972356001

I'll get me coat -- I'm off to the pub... :)

@ mad hacker

yes, quite obviously, that entire paragraph was completely re-written following my rant

it originally talked about dynamically varying the drive speed

a or an

he is right that its entirely down to the sound rather than the specific letter,

the easiest example is:

an MP

even though M is not a vowel, in this context it is pronounced:

em-pee

so its "an em-pee" :P

How do folk back these up?

There seems to be the usual foolish confusion between RAID and backup here.

RAID mirroring (or to a lesser extent RAID5) gives you protection against a hardware failure making data unavailable.

In a full time RAID setup, what protection is there against data being unintentionally corrupted or deleted by the user, by an app, or by the OS? None.

If I had one of these, I'd want two of them, not in any kind of RAID config. And every now and then, I'd use some kind of file sync program to sync the copies of the data. In that way, there is some kind of window when an unintentionally damaged file can be restored from the backup. OK the intact copy may get overwritten if the damage isn't noticed before the next sync point, but only if the sync program doesn't ask for confirmation before overwriting the old copy...

Pricing is good, I'm getting 4.

Just got a firewire drobo and shoved a load of spare old 500GB drives in there to act as a temporary backup for only my most important folders.

However, I've also wanted to be able to keep backups of all my dvds and animation work as well... some of the render outputs (particularly the folders containing 2500+ 1920x1080 TIFF files) are currently too big to be able to backup now that I've had to start making HD content.

Glad to hear it's quiet, too.. would rather not have 4 little rasping dinosaurs spinning away behind my desk when the backups are taking place.

1TB drives were not quite enough to offer a complete solution to all my backups needs, so I didn't bother upgrading.. 2TB does the job nicely.

I can't see myself needing a 4TB drive for a long time... unless something crazy like a new "superHD" standard comes along.