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January 8th, 2016 13:00
MD3620i High Latency And Low Throughput
Hi Everyone, I have a big issue and was hoping someone can shed some light. We have a dual controller MD3620i with 22 disks in one disk group running RAID 6. Drives are 900GB 10k RPM SAS. On top of this we created a single virtual disk with a little over 16TB of space. The SAN is directly attached to a Poweredge server running Server 2012 R2 using an Intel x540 dual port 10gbe network card. Port 0 on controller 1 connects to port 0 on the Intel NIC, port 0 on controller 2 connects to port 1 on the NIC, both connection use short CAT6a cables. The virtual disk was presented to the server using iSCSI initiators and MPIO is enabled. The virtual disk shows up as a 16TB D: drive on the windows server. The issue is, performance is terrible. Copying files from this volume we get 40MB/s, task manager shows active time to be almost 95% and average response time time for the disk at 500ms. During transfers our cpu spikes and we see System Interrupts using anywhere from 5-10% of cpu. With this many spindles we should be flying. The SAN and the Intel x540 both have the latest firmware and drivers. Any ideas? Thank you.
tgedgau
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January 13th, 2016 13:00
Thanks for the input Sam, but I respectfully disagree. These are 10Gbe connections so we should see a theoretical 1GB/s of throughput. When we first ordered this unit, it came with only 12 drives. We created the RAID 6 disk group and presented it to the server. CrystalDiskMark was showing 900MB/s read and write speeds. We were very happy with those numbers. After adding 10 more drives to the disk group we now see 70MB/s reat and write speeds. Nothing has changed in regards to the configuration or number of connections to the server. Only thing that changed was the expansion of the disk group by 10 additional drives.
DELL-Sam L
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January 13th, 2016 13:00
Hello tgedgau,
With how you have described your setup I think your issue is with the connections to the server. You need to have at a minimum of 2 connections from each controller to the server. Since you currently only have a single connection to the server from each controller that is why you are getting such slow performance. Also with only have a single connection from each controller you are not getting mulitpathing or any HA as it only seeing a single path. I would add a second connection to each controller & that should improve your performance & through put.
Please let us know if you have any other questions.