William "Chops" Westfield wrote:

>> He argues that RAID typically reduces reliability. ie done well it can
>> be an improvement, but ... .
> 
> For Raid0 (striping), he's clearly right.  Double the potential for
> failure. 

Agreed.

> For Raid1 (mirroring), I'm less sure.  He seems to be comparing "real"
> raid experience with "ideal" backup plans, and I'm not sure about his
> claim that a disk failure in a raid1 "means a long frustrating hassle."
> (It's not supposed to, is it?  Swap out the bad drive, add in the new
> drive, let the mirror re-build?)  And I suspect we're all aware of just
> how difficult it is to maintain that 'ideal backup plan.' 

Also agreed. 

I don't think it makes sense to talk about "RAID" in the generality that
he's using.

First, there are many different RAID setups, with different objectives.
It's somewhat comparable to saying "paralleling MOSFETs is not good".
(Perhaps... you know, analogies... :)

Then, there is hardware RAID and software RAID. For hardware RAID, you
definitely need think carefully (and up front) about how to replace your
controller once it's broken. It's now part of the necessary infrastructure
to access your data. Software RAID doesn't suffer from that drawback.

And third, RAID is no replacement for a backup strategy, it's a complement.
It doesn't help you get the file back that you accidentally deleted or
changed. 

The harddrive failure rates he cites are bogus (or at least incomplete).
What does "%" mean? Harddrives do fail, and you never know when it's time
for yours. May be today, or in twenty years. Or later still -- but you
don't know until it fails. And a RAID1 (or similar redundant config) array
lets you continue your work without (immediate) interruption -- and only a
short delay at a convenient time for replacing the defective drive and
initiating the rebuild of the array. In the meantime (while one drive is
broken), it's no worse than a normal drive.

I'm a fan of software RAID1 (integrated into a decent backup strategy, of
course). Very little extra cost for a huge increase in peace of mind.

> I'm starting to think about a new desktop for myself, and was thinking of
> a raid 5 array (it's looking less likely; I was hoping for a software
> raid5, and it doesn't look like that's actually supported.  

I'm not sure software RAID5 makes sense. There seems to be a lot of
overhead involved with RAID5. I also think that the advantages of RAID5
compared to RAID1 for normal desktop/home server use are not significant.

Gerhard

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