As Aleksander says, block-level backup can also be accomplished by using RAID-1 and using the secondary drive(s) as the backup media. You can then "fail" the secondary drive(s), pull them out, replace them, and ask your RAID to rebuild the secondaries. This is very, very clunky and I do not recommend doing it--but it is an option.
Actually, what I had in mind were Solaris boxes that have some extra features (such as offlining, three-way mirrors, and file system locks). And certanly nothing like failing the drives or ripping them out ;-)
Something along the lines:
# /etc/init.d/my-apps stop # lockfs -fw /mount/point # metaoffline d10 d11 # lockfs -u /mount/point # /etc/init.d/my-apps start # ufsdump 0f /dev/rmt/0n /dev/md/rdsk/d11 # metaonline d10 d11
If d10 was two-way mirror (the only kind of mirror available on Linux), redundancy is lost during backup. If it was three-way mirror (Solaris has support for it), redundancy is not lost (but you need 50% more of disk space compared to two-way mirroring, oh well). Plus, example above uses offline/online commands (not dettach/attach). When d11 is onlined, only changed disk blocks are synced (not entire partition). AFAIK, Linux lacks support for lockfs and online/offline operations. So for large partitions on Linux this isn't a good option (huge detached/reattached partitions can take hours to sync on Linux, while offlined/onlined partitions on Solaris can sync very fast, depending on how many writes were to the disk while submirror was offlined).
-- Aleksandar Milivojevic <amilivojevic@xxxxxx> Pollard Banknote Limited Systems Administrator 1499 Buffalo Place Tel: (204) 474-2323 ext 276 Winnipeg, MB R3T 1L7
