Dumb filesystem idea

Atom Powers atom.powers at gmail.com
Mon Feb 5 05:23:42 UTC 2007

On 2/4/07, Indigo <indigo at voda.cz> wrote:
> Hello Everyone,
>   Im about to try a disklayout experiment and I wanted to ask everyone if
> Im trying things that are pointless or if I should extend the experiment
> somehow.
> Hardware:
>   Highpoint RocketRAID 2320
>   2xWD Raptor 74GB
>   5xWD Caviar 320GB
> Original idea for the setup:
>   74GB RAID1 (Raptors)
>    /,/var,/usr
>   50GB RAID0 (Caviars[10GB from each - maybe less])
>    swap,/usr/obj,/tmp,[/var/audit]
>   1TB+ RAID5 (Caviars[the rest])
>    /home (or just general storage)
> The goal is to waste as few fast/reliable space as possible on things that
> CAN be lost and to generally reorganize the filesystem by file purpose.

It looks to me like you are wasting system drive channels. That is,
IDE can only have two drives per channel, SATA can have one drive per
channel. SCSI is too expensive to waste on 10GB drives. So while you
might be moving low-use data off of a high-use file system you are
losing the ability to have a high-capacicy file system.

> Known issue is that I'll need some script to recreate the RAID0
> filesystems when they crash.

Shouldn't be a prolem with gvinum. Except that some applications
/will/ crash if /tmp dissipears, and you certainly don't want swap to
dissipear if it's being used either.

> Am I onto something here? I feel like running in circles - it's dumb to
> put /var/obj on the RAID1 where it just eats valuable space. But it's also
> dumb to put things on a RAID0 where they will crash a running system in
> the event of disk failure. I know my idea won't work but I wanted to ask
> if anyone was playing with similar ideas.

The trick is to balance your performance requirements and your fault
tolerance with the data usage and system security requirements. The
fault tolerance of RAID 1 and RAID 5 are nearly the same, each can
survice exactly one drive failure. In your example above, the Raptor's
are fast, but depending on what the system is used for you might need
that speed in /var, swap, or some other mount point, most of the time
IO on / and /usr is pretty low. On the other hard, RAID 5 is fine for
a file server, but if you have a database on that volume you might
want to go with RAID 10.

So no, your idea isn't dumb, you just didn't give enough information
to make a meaningful assessment.

Perfection is just a word I use occasionally with mustard.
--Atom Powers--

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