high disk queue lengths and latency on iSCSI volume used for file sharing - Netgear ReadyNAS 2120
Posted on 2014-03-25
We have a Dell Equallogic P4000 with 16 x 600GB 15k SAS drives in a
RAID 50 configuration. Separate LUNs for VMs, SQL DBs, and file data. All LUNs are accessed via iSCSI on a separate dedicated network than LAN data. Everything has been working well. I started running low on space so on wanted to offload the file data to a different storage device. I chose a Netgear ReadyNAS 2120. I'm beginning to regret my choice. There are four 2 TB 7200 RPM SATA drives in a RAID 10 config. I have a single LUN configured for iSCSI. I moved all the file share data off the Equallogic volume to the Netgear volume. The same file server managing all the shared folders is in place. It has a dedicated network interface for LAN traffic and one dedicated for iSCSI. Ever since I did this, our clients are saying performance is horrendous. Sometimes it takes 30 seconds to open a file, then the next file opens right away. Seems to be intermittent. But one thing is certain, it's been really bad since moving data to the Netgear. Did I just make a bad decision with the Netgear? Before I migrated, I tested by copying large files back and forth and comparing that with copying to and from the equallogic. File copy speeds were identical. I know the drive RPM is half, and going from SAS to SATA, but I wouldn't expect it to be this bad for simple file sharing. I have opened a support case with Netgear - they are still analyzing the logs. The NIC settings are the same as they were when connected to the iSCSI volume on the Equallogic. Should I try changing settings like MTU, large send offload, TCP offload, etc? Or should I just chalk it up to a low quality NAS device? Please let me know if you have any ideas for improving performance.