RAID Controllers, Performance Issues and drivers.

[kayotee]

Hi Everybody,

I' ll beging by admitting that I am new to VMware.

I decided to build a standalone ESXi 4.1 server based on Intel's S5520HC board.

http://www.intel.com/products/server/motherboards/s5520hc/s5520hc-overview.htm

I used 5 Seagate 1TB SATA HDD 7200rpm 32MB cache connected to the MB controller. Of course ESX could not see the RAID so I used this:

http://www.intel.com/products/server/raid-controllers/SROMBSASMR/SROMBSASMR-overview.htm

I connected the 4 HDDs in a RAID 10 conf and used this driver during installation in order for this controller and R10 array to be recognized.

http://downloadcenter.intel.com/Detail_Desc.aspx?agr=Y&DwnldID=18453&ProdId=3148&lang=eng&OSVersion=...

I installed ESX on the 5th drive and also assigned the spare capacity as a 'scratch' datastore. I configured ESX to use this datastore as swap for the VMs. I also added an iSCSI datastore on a homebuild storage based on Openfiler using similar drives (RAID 10 setup) . All net connections are Intel gigabit on 3Com gigabit switches. So we have 3 datastores. 1st is on a single drive, 2nd is on hardware RAID10, 3rd is on gigabit iSCSI. The read and write performance of the 2nd datastore was dire. It was much lower from both other datastores. (read or write would not exceed 20000kBps as seen on vSphere client performance tab.

I decided to swap the controller with on that is natively supported by ESX, so I used Intel's RS2BL080

http://www.intel.com/products/server/raid-controllers/RS2BL080/RS2BL080-overview.htm

so I used 4 same drives and RAID 10 setup and the performance was even worst.

I noticed that ESX used the same driver from the 1st controller since they are compatible. (megaraid sas)

I would like to permanantly unload/remove this driver and let ESX use its native one, without reinstallation of course.

All other suggestions in order to improve performance are most welcome.

Thanks.

[a_p_ · Accepted solution]

Welcome to the Community,

it's not the driver which matters, it's the write mode in which the RAID controller operates. RAID controllers usually operate in write-through mode unless they have a battery-backed cache module attached. With the battery-backed cache module they are able to operate in write-back mode which basically boosts performance. ESX(i) fully relies on the caching of the RAID controller and does not do any software based caching for security reasons.

Usually you will see transfer rates between 5-20 MB/sec in write-through mode and >80 MB/s in write-back mode.

André

[kayotee]

Thanks Andre for your swift reply.

You are right of course about the write cache modes.

Your answer prompted me to dwelve a bit deeper into the controller manuals (If all else fails RTFM!! )

Since this is my 1st time working with Intel RAID controllers, I did not notice that cache settings in general are not implemented as a global policy ie in the controller properties section, but individually per virtual drive. Gone into BIOS, changed write cache to write-back and read cache to read-ahead, as well as enabled the physical drive cache.

Performance increased considerably I do get now more than 80MB/s.

BTW If you do not have a battery installed on the controller you just get a warning about possible data loss. The server though is supported by UPS so the risk is minimized anyway.

Thanks again.

[a_p_]

You are welcome and thanks for the feedback.

Gone into BIOS, changed write cache to write-back and read cache to read-ahead, as well as enabled the physical drive cache.

Usually you would not enable the physical disk drive's cache with the cache enabled on the controller.

BTW  If you do not have a battery installed on the controller you just get a  warning about possible data loss. The server though is supported by UPS  so the risk is minimized anyway

It depends on the controller whether you are able to enable write-back without a battery. Most controllers allow it (with a warning), but some don't.

André