On Dec 28, 2005, at 10:51 PM, Jarod Wilson wrote:
On Wednesday 28 December 2005 22:37, Brad DerManouelian wrote:
On Dec 28, 2005, at 10:30 PM, Yeechang Lee wrote:
To make a long story short, my 2.8TB JFS-on-LVM2-on-software RAID 5
array has certain mysterious performance bottlenecks that result in
7.5-10MB/s local write speeds, despite eight spindles and two 3Ware
7506 controller cards in JBOD mode and on separate buses and with
iowait never going above a few percentage points at the very
most. Over the network that's even slower, of course.
This actually sounds pretty typical of RAID 5 to me. Every write
results in 2 simultaneous writes. Even slower when you're doing it in
software. Great for redundancy, terrible for throughput. That's the
trade-off.
Erm, software RAID 5 isn't *that* bad. I've got a sw RAID 5 array
that only
consists of four ATA drives, and can write at a sustained rate of
30MB/s
without a problem. I've got a 5-drive U320 software RAID 5 array in
another
machine that does ~80MB/s without a problem.
My point is that RAID 5 is *MUCH* slower than just about any other
RAID config and you should expect your max speed to be half of your
fastest drive. Put those U320's on RAID 0+1 and you'll likely double
your speed (and half your recoverability). That being said, the
original poster obviously hasn't got that kind of throughput and RAID
5 is cutting whatever he has in half.
Yeechang, what kind of drives are in your RAID 5? ATA-133? 7200 RPM?
8MB Cache?
-Brad
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