On 18/07/2013 17:39, Grant wrote:
Basically run dump or something on the client, to a holding disk file on
the server with the tape. I don't see any issue with temporary disk
use. The point is that all the temp bits are written anew each time,
not assumed to be the same based on metadata.
So what we are trying to avoid is always copying data from the client
to the same blocks on the server's HD before copying to tape? We want
to copy to random blocks on the server each time so we aren't always
stuck with the same bad blocks?
And you don't try to maintain a special (rdiff-backup, rsnapshot, etc)
repository on tape, you just keep recording full copies and changing
tapes?
We can't just use fsck on the HD to check for corruption?
There is logic in having a simple ol' backup under lock and key, but I
would say do that alongside rdiff-backup for onsite backup, replicated
offsite with rsync. Yes there is a theoretical risk of corruption of the
primary (onsite) backup (which would then be replicated offsite), but
rdiff-backup always stores the most recent backup set in the clear and
this would be quite easy to verify against the source data with rsync
using -c (checksum) option.
For older version of files (or a file that no longer exists on the
source) the risk of corruption increases I admit. rdiff-backup does
offer a verification routine for earlier backups but I believe you
should run it for each separate backup sequentially to have high
confidence that all data is recoverable. I have a script which can help
with this.
In practice I don't do this regularly but using rdiff-backup I have
recovered database files from 6 months ago that have subsequently been
backed-up daily and have changed each day. The thought of going from the
current backup and applying each reverse-delta file sequentially to
recover the version that existed 180 days ago makes my brain hurt, but
rdiff-backup has patched it all up seamlessly...
Dominic
http://www.timedicer.co.uk
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