Rahul Nabar wrote:
If I have a option between doing Hardware RAID versus having software raid via mdadm is there a clear winner in terms of performance? Or is
Depends upon workload, writes vs reads, streaming vs random IO, number of simultaneous readers/writers. There is no real clear answer.
the answer only resolvable by actual testing? I have a fairly fast machine (Nehalem 2.26 GHz 8 cores) and 48 gigs of RAM.
Testing is a good thing. Sadly, too many people test *after* they purchased something (only to discover what is meant by the term "marketing benchmark numbers").
Should I be using the vendor's hardware RAID or mdadm? In case a
Ohhh ... it depends. Some of the "vendors" hardware raid ... heck ... most of it ... is rebadged LSI gear. Usually their lower end stuff which is sometimes fake-raid. Use fake-raid only if no other options exist.
More in a moment.
generic answer is not possible, what might be a good way to test the two options? Any other implications that I should be thinking about?
Benchmark your load using a load generator like fio.
Finally, there;s always hybrid approaches. I could have several small RAID5's at the hardware level (RIAD5 seems ok since I have smaller disks ~300 GB so not really in the domain where the RAID6 arguments kick in, I think) Then using LVM I can integrate storage while asking
RAID6 kicks in purely from the second correlated disk failure scenario. This is size independent. It happens, and you need to be prepared.
LVM to stripe across these RAID5's. Thus I'd get striping at two levels: LVM (software) and RAID5 (hardware).
LVM is not a performance tool. Use it to help you manage things, not speed things.
Our own testing puts our 24 bay DV4 unit at a bit more than 1GB/s sustained read (large block sequential) in RAID6, with writes in the 400-500 MB/s region (large block sequential). This is MD RAID based. Our "equivalent" JR4 system clocks in at nearly double the read speed, and about 3+ x the write speed. This is a hardware RAID system.
Your mileage will vary ... tremendously ... as a function of your IO pattern.
My own suggestion is to test before you buy. After you buy, well, its a bit harder to change your mind.
Joe -- Joseph Landman, Ph.D Founder and CEO Scalable Informatics, Inc. email: land...@scalableinformatics.com web : http://scalableinformatics.com http://scalableinformatics.com/jackrabbit phone: +1 734 786 8423 x121 fax : +1 866 888 3112 cell : +1 734 612 4615 _______________________________________________ Beowulf mailing list, Beowulf@beowulf.org sponsored by Penguin Computing To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
