UCS C210 M2 RAID Performance Issue

[rbass]

Hi all,

We have a C210 M2 Server with LSI 6G MegaRAID 9261-8i Card and factory shipped SAS Extender (up to 8 drives support).

We have 2 x 73Gb SAS 15K RPM Drives, and 5 x 600Gb SAS 10K RPM Drives.

We have setup a RAID 1 with the 73GB Drives and a RAID 5 with the 600GB drives managed by the MegaRAID card.

Whilst the configuration works, it is VERY slow. However, we have found that if we reduce the RAID 5 config from 5 to 4 drives the performance improves dramatically!

So my questions are;

1) I know there are two cables each attached to a bank of 4 drives but is this then a limitation to the number of drives you can have in a RAID 5 or can the the controller card SPAN the two banks of drives?

2) If the RAID can span over the 2 banks of drives what other configuration settings or tweaks do I need to do so we can get good performance from the deired configuration of RAID 1 + RAID 5?

Many thanks for your help.

Rod

[padramas]

Hello Rodney,

1) I know there are two cables each attached to a bank of 4 drives but is this then a limitation to the number of drives you can have in a RAID 5 or can the the controller card SPAN the two banks of drives?

LSI 9261-8i card can support 3 to 32 drives in RAID 5 configuration and can span across the backplane ports.

RAID 5 Overview, page 30

http://www.cisco.com/en/US/docs/unified_computing/ucs/3rd-party/lsi/mrsas/userguide/LSI_MR_SAS_SW_UG.pdf

http://www.cisco.com/en/US/products/ps10493/products_data_sheets_list.html

Can you please let us know how do you measure the RAID perrformance ?

Padma

[chrism]

Hi Padma,

I am measuring RAID performance using primarily CrystalDiskMark.  The main issue is with sequential write performance.  I've found that in a RAID 5 configuration with 5 drives the write performance is in the ballpark of 25-30MB/s.  When configuring the RAID 5 with only 4 drives, performance increases substantially to 380-400MB/s!

I am trying to determine if there are any other factors that could be causing this kind of performance degradation but I was hoping Cisco may know how to best configure a RAID 5 on this server.

Sincerely,

Chris Morgan

BASScom

Systems Engineer

[chrism]

I may have been premature in my assessment of the problem.

Now when using either 4 or 5 drives in RAID 5 I am consistently getting poor write performance.

Tested today using CrystalDiskMark and ATTO Disk Benchmark.

I have tried different combinations of drives, changed slots, changed different Virtual Disk properties but the problem remains.

At this point I am unsure what the cause is.

Chris

[padramas]

Chris,

RAID performance depends upon number of factors.The following LSI doc could be used as reference sheet.

http://www.lsi.com/downloads/Public/Direct%20Assets/LSI/Benchmark_Tips_Jan_2010_v2_0.pdf

As per MegaRAID SAS User Guide , RAID 5 does not provide good write performance.

( Table 16: RAID Levels and Performance ,Page 38 )

Can you let us know the stipe size and write policies in your setup ?

Padma

[billi]

Disk array performs better with disk cache turn on. Make sure disk cache is on in your array config.

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