Winnie,
I've also wondered about this, so I asked John here at L'pool. He told me
that, with sw raid, the thing that matters logically is that the
partitions that
are used in the raid setup are equal in size. It will still work even if the
media, interfaces, buffer sizes and speeds differ. Depending on which
disk is
accessed, you may suffer a speed hit. The situation is different with
hardware
raid cards, I am told. The extra space on the bigger disk is wasted, whereas
in a s/w raid setup, you can put extra partitions on it and use them for
whatever you like.
On the other hand, it's always nice to have similarities in your hardware,
so that you can manage the spares easily. In that sense, it is safer.
But (let me put it this way) we don't think there is any inherent danger
because the disks are mixed. I'd welcome other views, of course.
Steve
--
Steve Jones [log in to unmask]
Grid Administrator office: 220
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University of Liverpool http://www.liv.ac.uk/physics/hep/
Winnie Lacesso wrote:
> Dear All, got a hardware q.
>
> Most of our important servers have a pair of Linux software RAID1 OS
> disks. In looking into buying spares, it's impossible to match specs - for
> instance our Viglen servers came with 2 x WDC WD2500YS-01S = 16MB, AvgLat
> 4.2, AvgSeek 8.7, Internal Data Rate 70MBps.
>
> You simply can't buy a match, new disks have much faster Internal Data
> Rate. The old-ish 250GB replacement we have on hand is a WD2502ABYS with
> same buffer, AvgLat & close AvgSeek, but an Internal Data Rate of 126MBps.
>
> A set of other 250GB disks (at Insight) all only have 8MB Buffer, similar
> AvgLat & AvgSeek (altho some up to 14ms) but Internal Data Rates varying
> 95-110-125MBps to 140MBps.
>
> In such close work as RAID1, how much will those differences matter, or
> will the faster disk throttle back to match its slower older mate? And
> what about an 8/16 difference in buffer size? Bad or doesn't matter?
>
> It would be bad for the RAID1 to become unstable.
> An option is to have 2 spares, remove damaged drive, sync with
> replacement, then also remove the other old one & replace with new &
> resync so the RAID1 pair is always identical disks. Safest, or just
> unecessary work/caution?
>
> Grateful for enlightenment.
>
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