Re: What is the point of RAID?
On Wed, Nov 12, 2008 at 06:39:09PM -0600, Boyd Stephen Smith Jr. wrote:
> On Wednesday 12 November 2008, lee <lee@yun.yagibdah.de> wrote about 'Re:
> What is the point of RAID?':
> >On Wed, 12 Nov 2008 09:59:09 -0600
> >"Boyd Stephen Smith Jr." <bss03@volumehost.net> wrote:
> RAID-5 might not be the fastest or least risky way to store data across
> 5x(1 TB) drives, but it wins because it gives a lot of space (4 TB) at an
> acceptable level of redundancy -- I challenge anyone to come up with a
> scheme that gives the same performance and at least 3 1/3 TB of space with
> ANY redundancy.
>
The other thing to consider as that you don't necessarily need the same
performance/protection for the whole dataset on a system.
Having the OS live-redundant (e.g. raid) makes a lot of sense. However,
at some point, you have to consider that if downtime (as opposed to data
loss) is so problematic you need to consider failures other than drives,
which leads to some type of high-availability system.
Just sticking with the data, for now:
Data that needs to be always live, e.g. transaction data, raid makes
sense. Non-transaction data (think archives, documents, movies, etc),
where you can tolerate inaccessability for the duration of a restore,
then just relying on solid backups makes sense. If those backups are on
disk-type media (e.g. external hard drive, virtual tape server,
whatever) then restore is very quick. If those backups are on tape,
then it takes a bit more time.
There's no reason why you couldn't have /home on raid (so that no matter
what the drives were doing, you'd be able to log in and get some work
done), but have a non-raid filesystem mounted on, e.g.
/var/local/archive with directories for each user just like /home. The
user could symlink them into a directory in their ~/ directory. If the
~/ directory was limited in size (quota) but the ~/archive/ wasn't, then
they'd have an incentive to store their videos in the archive.
/var/local/archive could then be back-ed up frequently but not
necesarily be raided. The greatest advantage here is if the data files
in the archive aren't already compressed, in which case the backup
procedure compresses them and the backup takes up less capacity than a
raid array.
Just a thought, with the same disclaimer as a previous poster gave.
Doug.
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