Messages in this thread | | | Date | Tue, 15 Dec 1998 12:59:50 +0000 (GMT/BST) | From | Mike Jagdis <> | Subject | Re: SMP 2.1.131: SCSI performance extremely poor vs. IDE |
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On 14 Dec 1998, Camm Maguire wrote:
> 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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