> Greetings! I'm running 2.1.130, SMP, 2 PII 350, 128 MB RAM, Adaptec
> 7890 U2 wide, 2 Seagate ST39173LW "Barracuda" drives.
> [...]
>
> In any case, I'm not getting anything like these numbers. Basically,
> I don't see any noticeable improvement with RAID, except maybe for
> seeks. I haven't tried RAID-0 yet, just RAID-1, but I thought that
> could double the read performance.
Have you experimented with different RAID chunk sizes? The way
accesses are distributed across disks in RAID 0 or 1 pairs
tends to mean that, for sequential access greater than the
chunk size, you read n sectors, skip n sectors, read n sectors, etc.
This interacts badly with some drives caching strategies.
As I mentioned in a previous message my own experimentation
with a pair of Seagates (ST15150s) show that a chunk size of 32k
pretty much doubles the throughput when they are paired in a
RADI0 group. *Any* other chunk size causes such a collapse in
throughput that it is barely better than a single drive could
manage. It sounds like this is what is happening to you.
Mike
--
A train stops at a train station, a bus stops at a bus station.
On my desk I have a work station...
.----------------------------------------------------------------------.
| Mike Jagdis | Internet: mailto:mike@roan.co.uk |
| Roan Technology Ltd. | |
| 54A Peach Street, Wokingham | Telephone: +44 118 989 0403 |
| RG40 1XG, ENGLAND | Fax: +44 118 989 1195 |
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