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MSA20 Performance

Jeff A.
Occasional Visitor

MSA20 Performance

The MSA20 Q/A states a max tranfer rate of 150MBs.

So, can anyone explain the internals of the MSA20? Is the entire 1.5Gbs SATA bandwidth shared between all 12 drives? (no point-to-point I assume..) I noticed there are 2 "ports" in the ACU, 8 drives on one port, and 4 on the other. I couldn't see any performance differences splitting drives between ports.

Running a 250GB SATA x 12 drive Raid 10 array on the MSA20, I can get 800 IOPS on small random reads, but big sequential reads and writes are always capped around 90 MBs. I've tried 4 and 6 drive Raid 10 configs, even Raid 0. IOPS figures change accordingly...but 90MBs seems to be the upper limit on sequential reads or writes.

If I have two MSA20 cages, and run 6 drives from each cage in Raid 10 can I expect to get 180 MBs?

Purhaps I need an MSA60. What kind of throughput could I expect on an MSA60 with a 12 drive SATA Raid 10?

Thanks,
Jeff
6 REPLIES
John Kufrovich
Honored Contributor

Re: MSA20 Performance

Hello Jeff,

A couple of items need to be straightened out. All SAS/SATA technologies are point to point. 150MB/s is derived from 1.5Gbs, with serial IO all bytes are 10bits. So, 1.5Gbs translate to 150MB/s.

I would say 90MB is about max out for sequential performance. If you are using direct attached SA64xx controllers you can enable the physical write cache on the HDD. Just use ACU. These will speed things well beyond 90MB/s. I would only recommend using the setting if you have a UPS.

Also, keep in mind, SATA 1.5Gb or SATA generation 1 has no command queuing, so all transactions are FIFO. This can severly limit random performance.

jk
Jeff A.
Occasional Visitor

Re: MSA20 Performance

What about write caching performance connected to an MSA1500?

Some further benchmarks seem to indicate lack of write caching. Batteries are good and caching are enabled on both MSA20 and MSA1500 50%Read/50%Write.

Here are some IOmeter results, queue depth 16, 250GB SATA drives. Quick runs, but figures should be pretty close:

Single Drive:
4K Rand: Read 80 IOPS / Write 90 IOPS
128K Seq: Read 60 MBs / Write 10 MBs

2 Drive RAID 0:
4K Rand: Read 148 IOPS / Write 150 IOPS
128K Seq: Read 120 MBs / Write 21 MBs

3 Drive RAID 0:
4K Rand: Read 213 IOPS / Write 231 IOPS
128K Seq: Read 132 MBs / Write 32 MBs

I could continue with more drives, but you get the idea...can't get any drive to write faster than 10MBs.

Thanks,
Jeff
John Kufrovich
Honored Contributor

Re: MSA20 Performance

On all SAN storage the write cache is turned off on the drives. This is to protect the integrity of the data in case of power loss.

Realize that all drives have a mechanical limitation on number of IOPS. You can calculate the seq max IOPS.

SATA
7200/60 = 120 IOPS, perfect world. Add journaling FS and other OS stuff, your IO will drop. SATA 1.5G drives are FIFO's.

Take that 120 x 64k (block size) = 7.68MB/s.



Jeff A.
Occasional Visitor

Re: MSA20 Performance

That explains it. I noticed write performance for the MSA20 on the SAN was much lower compared to a directly attached MSA20.

Is there any way to enable writeback caching on the MSA1500? We have a UPS, so power outages are not an issue. Our restore times are taking too long.
Patrick Terlisten
Honored Contributor

Re: MSA20 Performance

Hello,

the write cache is always battery backuped in a MSA1000 / MSA1500cs. If you're using a Smart Array controller, add a BBWC module.

Normally the cache is devided into 50% read and 50% write cache, you can control it with ACU, just take a look in the controller-settings.

Best regards,
Patrick
Best regards,
Patrick
John Kufrovich
Honored Contributor

Re: MSA20 Performance

Jeff,

There is no way an individual can enable the write cache on the drives.

A MSA20 direct attached to a SA64xx will allow an individual to enable the write cache to the drives.

jk