Re: Periodic refresh (or rwrite?) of data on an SSD (was: Re: Recommended SSDs and 4-bay internal dock)
Jeremy Nicoll wrote:
> On Fri, 13 Jan 2023, at 15:33, rhkramer@gmail.com wrote:
>
> The whole issue makes me wonder if, say, I should plan on having several
> SSDs for each set of backup data (I mean separately from the common-
> sense approach of having more than one copy of anything anyway). Then
> every n weeks, delete the data from the least-recently written drive and
> copy a fresh copy (from the most recently written drive) onto that one, &
> verify that every file copied has the same hash as its original. (I suspect
> I'd want to keep lists of file hashes anyway, as a way of detecting when
> any backups start to go bad.)
>
> I'm not sure that that was clear. What I mean is that if I intended to keep
> a backup of a driveful of data, I might choose to have, say, this week's
> copy, last week's, and the week before. So apart from the original disk
> I'd have 3 other backup drives.
Let's separate the problem into three cases:
- I recently deleted some files, I want them back. (Same as "I
recently changed some files, I want the old versions.")
- I have lost a filesystem for some reason, I want it restored.
- I need to have archival copies of some data which I probably
will never access, but just in case...
The deleted/changed files problem is best solved, if plausible,
with a snapshotting filesystem like ZFS, with automatic
snapshots and automatic deletion of sufficiently old snapshots.
The restore-a-filesystem problem is best solved with a complete
filesystem copy to a similarly sized disk. SSDs are nice and
fast, but you may not actually need that speed if you don't have
to do a restore very often. ZFS send or rsync are good tools
here, or borg if you have special requirements.
The archive problem is best solved with spinning disks, which
are fast enough for most cases, much better priced per capacity,
and have well-understood stability over long periods of
unpowered time. Grabbing a copy from your restore-a-filesystem
system every so often might be the way to go.
In any case, think about backing up filesystems rather than
disks. Sometimes they are the same, but not very often.
-dsr-
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