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19072
August 5th, 2013 13:00
MD3000i appears to be only using 1 controller
We have been having some issues lately with disk performance in our VMware cluster. Our setup is as follows:
- 3 Dell R610's running ESXi 5.1
- 2 Juniper gigabit switches with 3 VLANs (1 for management, 2 for iSCSI)
- 1 dual controller Dell MD3000i
After troubleshooting for a while, I found I could use SMcli to monitor the performance of the SAN. Upon doing so, the results were somewhat surprising as it looks like one of our controllers seems to be completely inactive. I have taken a screenshot of the results: (Ignore the name of the storage array. It was previously used in a XenServer setup)
My question is, how do I get it to where both controllers are acting as a pair for best performance. I would think there should be some way to have the VMware hosts take the quickest path to either controller to get to the disk, is there not?
Any help would be greatly appreciated as this has stumped me for quite some time and searching the internet hasn't gotten me very far.
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Dev Mgr
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9.3K Posts
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August 5th, 2013 15:00
How did you carve up your virtual disks? The MD3k series use a single controller as owner for a virtual disk and the other controller is only for failover for that virtual disk. This is why running multiple virtual disks (that spread between the 2 controllers) is a better choice over a single max size virtual disk.
Also; the MD3000i is not validated for vSphere 5.x. This is unlikely to be the cause, but it is important to remember if you plan to run this for production (generally I'd recommend not to run production on this combo (upgrade to MD3200i or downgrade to vSphere 4.1)).
It is also important to use 2 subnets and have port 0 on both controllers on one subnet, and port 1 on both controllers on the other subnet. Each server then should have 1 NIC in each subnet.
Dev Mgr
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9.3K Posts
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August 7th, 2013 07:00
Raid 5 read performance increases with more drives, but raid 5 write performance decreases with more drives.
Most raid controllers typically achieve the best overall raid 5 performance with 6-7 drives in the raid 5. If your environment is pretty high on the writing (versus reading), then raid 10 will be a better choice, if you can afford the disk space loss.
You cannot change owner of a diskgroup, but you can change owner of a virtual disk. On one of the tabs you can see the virtual disks. Just right click on the virtual disk and there should be an option to change ownership.
adam.hahn
3 Posts
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August 6th, 2013 13:00
Thank you so much for the info! I had no idea that there was actually an "Owner" of the disk groups. I thought both controllers could access all of the LUNs simultaneously. In this particular setup we have 1 very large SAS LUN made up of 6 disks and 2 smaller SATA LUNs. We do have 3 subnets - 1 for management, and 2 separate subnets for the iSCSI traffic and the servers all have multiple NICs to connect to all 3 of the subnets, so we're good in that regard.
Currently all of the VMs are on the large SAS LUN. I did some research and thought I found that performance on a RAID 5 is increased with the more spindles that are present in a disk group. That is why I set it up this way. I completely understand that the MD3000i is not "supported', but unfortunately, this is all we could afford to go with and need to find some way to make it work.
Do you know offhand (or have a link) to how to change the owner of a particular disk group? I searched through the Modular Disk Storage Manager, but did not see anything related to changing which controller owns the disk group.
adam.hahn
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August 7th, 2013 15:00
Understood. Well, I can't thank you enough for the wealth of information! I will take this to the higher-ups and see which direction they would like to go.