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The Thursday 2007-12-06 at 17:51 -0600, Jim Flanagan wrote:
Thanks for the great discussion on this! In my case I'm running a home
server, that can be taken down for short periods of time when needed. I'm
more interested in maintaining my setup and data, so I set up a raid1 to give
me some redundancy here. That way if a disk encounters a problem between
backups, I have some built in protection. I usually do a full backup every
week, sometimes two, but not more than that. I don't have to have a failsafe
setup here, but would like to not loose data.
It is sometimes safer to have two disks not mounted as a raid, but a
backup, updated daily (or as needed) and then umounted. Why? Because if
you erase by accident a tree, or a program goes mad, or the kernel
crashes, you are not protected by a raid: both copies will go bad at the
same time. Raid only protects you from hard disk failure.
The reason I set up swap (and /boot, /, and /home) on raid was I was
following the article about software raid on the opensuse wiki. That article
indicated, and others I've read stated that in order to recover one lost disk
with the other, ALL partitions on the disk had to be mirrored (not just /home
for example). Is this true?
Well, all the partitions you /want/ to recover must be mirrored, of
course. But of course, you can mirror only partially a disk, and those
things that are mirrored are recoverable, not the rest.
For instance, a typical setup is to put the data on raid, but not the
system, because it doesn't change as often and can be recreated, perhaps.
I re-booted with the "noresume" option and can access swap now on the
mirrored /dev/md1 so that's not an issue now, and I'm comfortable leaving
swap mirrored on /dev/md1, but is that necessary or recommended? For
performance sake I could make swap not raid, but what does that do to my
recovery situation in the future if needed?
The need to put swap on raid is only if you need your machine to survive
running the same session as one of the disks goes bad. If you don't mind
your machine crashing once that single time - which may be once after five
years - then don't bother.
But I am still unclear on this. So to ask my remaining question more clearly,
can I recover a lost disk with the good one if it contains a mix of raid and
non-raid partitions on it, or does the whole disk need to be raid1 for
recovery?
You can of course recover the disk. The data that is mirrored can be
accessed and written to at the same time as the recovery to the new disk
takes place. The data on non mirrored partitions will not - but you can
get it from the backup.
- --
Cheers,
Carlos E. R.
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