[OpenIndiana-discuss] Broken zpool

[David Brodbeck]

On Wed, Oct 28, 2015 at 12:02 PM, Jerry Kemp <sun.mail.list47 at oryx.us>
wrote:

> From a high level view, his comment to them is to NOT run a mirror.  His
> suggestion to them is to just run a straight drive, then every evening or
> downtime, bring the other disk(s) online and sync them with the online
> master, using rsync, or your favorite utility, then once the sync is
> complete, offline the newly synced data and put it away.
>

I actually was going to suggest the same thing.  I hate to be a Monday
morning quarterback, but I think this is a really important point that's
often overlooked.

If you can only afford two disks, mirroring them is not the best way to
handle data security.  Even if you ignore filesystem corruption, think of
the simple case of accidentally deleting a file.  A mirror won't help you
because it'll be gone from both mirrors.

What you want in that situation is to use one disk for storage and the
other for backup.  This also ensures they'll have different usage rates,
which will probably lower the likelihood of a common flaw causing both to
fail simultaneously.  (If you can get disks that are different brands
altogether, so much the better.)

The way I usually explain it to people:

- Mirroring is for *reliability* -- so the system can keep functioning
during a disk failure.
- Backups are for data recovery.

Usually in a home situation you don't care that much about reliability; if
the server is down for an hour while you swap a disk it won't matter much.
Even at work I usually only use redundant disks in systems that are a
single point of failure for the network as a whole.

-- 
D. Brodbeck
System Administrator, Linguistics
University of Washington
GPG key fingerprint: 0DB7 4B50 8910 DBC5 B510 79C4 3970 2BC3 2078 D875