>>> I am running out of space on my root device and am thinking of adding
>>> another scsi disk using Raid - linear or 0 (whichever is the
>>> easiest!). Is software Raid as fearsome as all the docs I read
>>> suggest? Ideally, I'd like to be able to hitch the disk up, add a
>> At the same time, it's harder --- currently there is no way to take an
>> existing filesystem and simply extend it non-destructively using raid.
Not true.
Using linear, you can extend a *PARTITION* non (or almost non) destructively.
However, you also have to extend the *FILESYSTEM*.
You need the excellent (only commercial product I ever plug !) PartitionMagic,
or specifically the "resize2fs" (Linux) utility.
>> You will definitely have to find somewhere else to put the data while
>> you build the raid partitions.
That is the case for one of the "striping" levels (0, 4 and 5)
[ 1 doesn't help you increase the size of your FS ]
> Not entirely true. Leave the original data where it is. Build a degraded
> raid array on the new disk(s) and copy the data over from the old disk.
> Reconfigure to use the new degraded raid array, then hot add the old disk
> to the array. The kernel will reconstruct the data on an bring the raid
> up to snuff. This is how I converted a 2 disk raid 1 to a 3 disk raid 5.
> No reason why I wouldn't work from a standard partition, doesn't matter
> where the source data comes from or how the degraded array is initially
> constructed.
Sure, with RAID1 one can cheat by going degraded 1 -> degraded 5,
and the net result is a larger partition, but he's starting from a raw
partition ...
My sugegstion is to go for raidtools 0.90 (Persistent Super Block) and
0) use whatever means you have to boot a "rescue" system so that the root
device isn't mounted (I tend to start a network RedHat upgrade)
1) resize2fs the FS down a bit to make room for the PSB at the end,
2) mkraid the new linear partition (with PSB)
3) Ensure that /boot/ is a raw FS
4) resize2fs the new FS
5) set the partition type to 0xfd
and away you go ...
See http://www.idiom.com/~tbyrd/softraid/index.html for advice from one RAID
newbie to another ...
[[ but yes, if you're getting a new disk, I'd probably do it somewhat
differently, such as moving whatever is directly after the root FS
over to the SCSI disk,
or split off a chunk of the "root" disk, and put it on a new partition on
the new disk.
THEN I'd go for RAID1 of the new root FS for resilience :-)))
]]
