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View Full Version : Backups vs RAID



sixy
8th May 2006, 05:10 AM
I have a fedora 5 system that is running on a 250gb disk, partitoned as follows:
100mb ext2 /boot
<lvm>
4gb swap
20gb ext 3 /
~200gb xfs /home
</lvm>

there will be a large amount of data stored in /home, which has the potential to reach the 200gb limit and it is this data i am worried about. the actual system files can easily be replaced.

I have a second, identical, 250gb disk, and i want to make sure i do not lose that data if i can help it.

there are two options i have considered and these are:

1: raid1 array
for this i would probably reinstall the os (as there is as yet no data to be kept safe) and mirror the entire disk.
as budget constraints do not allow for a true hardware raid card, and as far as i know 2.6 kernels do not play nicely with on-board software raid controllers, this would be an mdm managed linux software raid setup.

2:regular scripted backups
the method i would probably use (unless you have a better) would be to freeze the /home filesystem, take a snapshot and unfreeze. then untar previous backup, update with rsync, and re-tar.

as far as i can see the advantages of the two options are:
1 produces least downtime as the entire system is protected against hardware failure, however no protection is offered against software/user problems (there is a good chance the end-users will delete a file the wish they hadnt. I can just say tough, but it would be nice not to)
2 offeres some protection agains software/user faults and also guards against hardware failure (although with more downtime involved) in the event of a system failure, as i would most likely run this script weekly due to high hardware demands, there is a higher chance very recent data will not be recovered. Also i am unsure if my desribed method would be possible if doing this operation on a 200gb folder given that the disk is only 250gb. does taking an lvm snapshot mean that that 200gb is stored twice, or is it stored once and linked to twice? also would the utar/rsync/tar be effective and work?

so there are the two options i have found. please rip them to shreds as much as possible, for this is a fairly critical operation.
also if there are other options that i havent thought of, please let me know.

many thanks for your help :D