I was given the task (aka dumped into my lap) to examine low Read/Write performance on a system running Server 2012 R2 /w HyperV role.

The system in question:

Lenovo RD340 LSI MegaRaid 9260-8i (no BBU) -Drive Group 0 consisting of 2 SAS Drives, each 279.397 GB, RAID1 -Drive Group 1 consisting of 3 SAS drives, each 558.912 GB, RAID5

Virtual machines are stored on drive group 1. VMs: Two domain controllers, a terminal server & an application server

It seems that read/write performance for drive group 1 is quite low. For example, when I try to export one of the VMs via HyperV Export onto the same drive (BYA: necessary for scripted exports), the max throughput is around 25~30 Megabytes/s. Seems low, especially in comparison to another system (Lenovo TD340 with LSI 9260-8i (with BBU)) where such an export nets around at least 150 MB/s and more.

Any idea what I should look out for to maximize performance?

Further settings for drive group 1:

  • Strip size 64 KB
  • Read Policy: No Read Ahead
  • IO Policy: Direct IO
  • Current write Policy: Write Through
  • Default Write Policy: Writhe Through
  • Current Access Policy: Read Write
  • Default Access Policy: Read Write

The "control group" drive group on the RAID controller in the TD340:

  • strip size 256 KB
  • Read Policy: Always Read Ahead
  • IO Policy: Direct IO
  • Current Write Policy: Write Back
  • Default Write Policy: Write Back with BBU
  • Current Access Policy: Read Write
  • Default Access Policy: Read Write

Thanks a lot!

  • 2
    You might need to enable write cache on the controller. As I remember, write cache is often disabled on non-BBU devices, as it could cause data loss if the device has a power failure. So beware of this if you have no UPS etc. – SteffenNielsen Oct 12 '15 at 9:49

From my measurements done a while ago on 9240 and 9260 LSI Megaraid cards in UCS servers the I/O perfomance using RAID 5 and 6 was significantly lower than in RAID 0 or 10, everything else being the same.

My suggestions would be (depending on the tolerance to failures in your context) either:

  • switching to RAID 0 (best I/O performance)
  • adding a 4th drive and switching to RAID 10

Using WriteBack instead of WriteThrough will boost write (and, depending on usage, even read) performance, regardless of the RAID type. It needs to be specifically enabled if you don't have a BBU or if it goes bad. A BBU is highly recommended :)

Finally I second @SteffenNielsen's comment about the write cache, also regardless of the RAID type.

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