Re: [gentoo-user] RAID 1+0 question

["Richard Fish" <bigfish@asmallpond.org>]

On 3/2/06, Marton Gabor <gabor.marton@vehok.vein.hu> wrote:
> Hi!
>
> Thank you all for the fast replies, you helped me a lot. Unfortunately
> we cannot afford a HW RAID card, so I have to make it with software RAID.
> Now I have the idea to use RAID5 and if I get the picure rigth I need
> let's say a ~100MB /boot in RAID1, 512MB swap not in RAID on every disk,
> and I can build a RAID5 from the rest of the storage space, and will be
> able to use 750GB-(/boot*4)-(swap*4) and the 4th HD will store the
> so-called parity information.

FYI, RAID5 will spread the parity information across all disks.

You should also consider what kind of IO throughput you require from
this system.  RAID5 will require an IO to every drive for each write
operation.  Additionally, reads can only be satisfied by a single
drive.  This means your write performance will max out at around
33MB/s, and reads will max out at the speed of the disks (70MB/s
typical today)

However writes to a RAID 0+1 array will only require writing to 2
disks, so your maximum bandwidth should be around 66MB/s when writing.
 Reads really benefit here however, since they can be satisfied by
either RAID1 set, so you should easily be able to saturate the bus
bandwidth at 132MB/s.

Of course, if you really need IO bandwidth, hardware RAID is best...

-Richard

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