What low end fibre channel rackmount RAID arrays will give me a consistent
20 MB / second average read and write speed with a reasonable number of 15K
RPM SCSI drives in a RAID 5 or RAID 6 configuration?

I've been using Compaq RA4x000 arrays as a cheap disk source for
applications that do not require very high disk performance.    I had
assumed the RA4x000 RAID systems would bottleneck on the 1 Gbit fibre
channel interface, which is far more throughput than I could get out even
six drives in a RAID 0 array.   Well, I was wrong.    I measured performance
today on a Proliant 6400R with 4 GB of memory, copying from a RAID 5 array
of five 15K rpm SCSI drives to a RAID 5 array with six 15K rpm SCSI drives.
Each array is located on a separate RA4x00 locally attached by a separate
Compaq FC 64-bit PCI card.   I am getting an absolutely miserable 2.5 MB per
second average write performance at the destination RA4x00 array.

How is the above result possible?   Each drive should pull data at minimum 3
MB per second, and five 15K drives in a RAID 5 should give me at minimum 10
MB/second read and write performance.   I don't have bottlenecks in system
memory, on the PCI bus, on the fibre channel bus.  I just don't see where
the 2.5MB/sec could be coming from unless it's hard coded into the array
itself.   I was measuring performance on the "physicaldrive" in Windows
performance monitor, read and write, on each drive defined by the separate
RA4x000 arrays.

With my commodity home-user SATA arrays I am getting 30 MB/second read
performance, over gigabit ethernet at that.    It just shouldn't be that
hard to find a business focused RAID array that can give consistent 20
MB/second or faster average read and write speeds?   What are my options?

--
Will

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"Bill Todd" <billtodd@metrocast.net> wrote in message
 news:36OdneA6NJx_hp_bnZ2dnUVZ_vCknZ2d@me
trocastcablevision.com...
> On the other hand, if you're transferring large contiguous chunks of data
> and still seeing this level of performance, then something is wrong with
> your array:  fix it, and it'll fix your problem.

The performance of 2.5 MB/sec average write speed was seen while reading and
writing a single 250MB file, and the file was all contiguous on a 72 GB
logical drive that had about 40 GB unused.   I examined the file's
allocation units on the drive with a file defrag application to verify that
everything was contiguous.

So it kind of does look like something basic is broken - possibly the array
just is not very good.   I did try copying in both directions from and to
the same array, so it's not a single bad piece of hardware.

--
Will

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In article < BpidnYYxEvemip_bnZ2dneKdnZydnZ2d@giganew
s.com>,
"Will" <westes-usc@noemail.nospam> wrote:

> What low end fibre channel rackmount RAID arrays will give me a consistent
> 20 MB / second average read and write speed with a reasonable number of 15
K
> RPM SCSI drives in a RAID 5 or RAID 6 configuration?
>
> I've been using Compaq RA4x000 arrays as a cheap disk source for
> applications that do not require very high disk performance.    I had
> assumed the RA4x000 RAID systems would bottleneck on the 1 Gbit fibre
> channel interface, which is far more throughput than I could get out even
> six drives in a RAID 0 array.   Well, I was wrong.    I measured performan
ce
> today on a Proliant 6400R with 4 GB of memory, copying from a RAID 5 array
> of five 15K rpm SCSI drives to a RAID 5 array with six 15K rpm SCSI drives
.
> Each array is located on a separate RA4x00 locally attached by a separate
> Compaq FC 64-bit PCI card.   I am getting an absolutely miserable 2.5 MB p
er
> second average write performance at the destination RA4x00 array.
>
> How is the above result possible?   Each drive should pull data at minimum
 3
> MB per second, and five 15K drives in a RAID 5 should give me at minimum 1
0
> MB/second read and write performance.   I don't have bottlenecks in system
> memory, on the PCI bus, on the fibre channel bus.  I just don't see where
> the 2.5MB/sec could be coming from unless it's hard coded into the array
> itself.   I was measuring performance on the "physicaldrive" in Windows
> performance monitor, read and write, on each drive defined by the separate
> RA4x000 arrays.
>
> With my commodity home-user SATA arrays I am getting 30 MB/second read
> performance, over gigabit ethernet at that.    It just shouldn't be that
> hard to find a business focused RAID array that can give consistent 20
> MB/second or faster average read and write speeds?   What are my options?

I've done a lot of write performance testing on SATA drives lately, and
750 GB Seagates consistently get 70-80 megabytes per second and that's
on their own. A 4-disk RAID 6 of these drives is similar, maybe a tad
quicker.

I'm bypassing its page cache (Linux) and using an 800 MB file which
overpowers the RAID card's own cache, but if I weren't bypassing the
page cache, the numbers would be definitely be better. It'd have no
trouble saturating a gigabit link.

Also, in my other setup, I have a failover cluster, which consists of
two systems each with their own SCSI to SATA based RAID 6 and I'm doing
network RAID 1 between them. That averages about 60 megabytes per second
to take data on one system and write it to both RAIDs.

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