[Dirvish] Expire or Archive?

Paul Slootman paul at debian.org
Wed Mar 15 15:24:18 EST 2006


On Wed 15 Mar 2006, Keith Lofstrom wrote:

> I could not answer his expire question, because I don't use it myself.
> I rotate drives, and when they fill up I retire them to archival
> storage and build new drives.   I do this about once a year.  That
> means I have daily images all the way back to dirvish day 1.  I have
> gone back to the archives a few times;  sometimes the history of files
> tells me about the history of a project.

I use it at home, and also at work. There we have more than a hunderd
systems that are backupped to one of three systems, each with 1TB of NAS
disk space. Default expiry is about 10 days, resulting in about 90% disk
usage in the backup systems. Images with much volatile data (web server
logs, for example) have shorter expiries.

> I worry that the cheap IDE drives that many of us use for dirvish may
> not last very long, and thus long term usage with expires may put the
> earliest archival copies at risk.  On the other hand, a drive sitting
> in storage may suffer from bit rot;  the magnetic information may
> decay if it is not actively rewritten from time to time.  On the
> third hand(!), files may get lost off of active drives, too.  Rebuilding
> new dirvish drives from time to time means that all files are getting
> completely copied.

Using S.M.A.R.T. tools to let the IDE disks execute selftests
(preferably at idle times) is very useful, in my experience it detects
badly readable sectors before they are not readable at all. Rewriting
those sectors will either "fix" the sector, or lead to it being replaced
by a spare. Depletion of the spare sectors will also be reported, BTW.

> How many of you are running expire, and how many are just archiving
> drives?  The expire feature is important and needs active development,
> but that will require contributions and testing by people that use the
> expire.  It is difficult to test if you don't normally use it!

Actually, I think the expiry feature is pretty stable as it is.
One thing that might be an improvement is some way of expiring images
depending on available disk space, so that you don't need to tune it by
hand.


Paul Slootman


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