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  • 1.  Bad write-performance on iSCSI SAN

    Posted Aug 01, 2013 10:17 AM

    Hello community,

    I've got a question to the following infrastructure: ESX 4.1 U1 on a HP ProLiant DL380G5 with the DLink DSN 2100 10 in iSCSI mode. The SAN is configured to present 3 LUNs to the ESX. The SAN itself has 8 x 1TB physical S-ATA disks running in RAID10 (configured by a third-party IT-Service provider). The physical connection between ESX and SAN is realised through 3x 1GBit/s with VLAN seperated Links. ESX is configured with multipathing and round robin to talk with the SAN.

    Whats my problem? My problem is the write-performance of the SAN! It's incredibly low (at about 10 MegaBYTE per second, round about 100MegaBIT/s). Read performance is very good, about 100 MegaBYTE/s / 1Gigabit/s)!

    It doesn't matter if I copy a file from VM to VM or just provision a new VM using vSphere Client. The write-performance is very bad!

    Can someone confirm that or has any other ideas? I'm beyond my ken with this issue!

    The last steps I did (it didn't worked before too): configure LACP / static Links on SAN side and on ESX, configured multi-pathing with all three available NIC's. Changed path-policy to Round-Robin. Any suggestions?

    Hope you can help me.


  • 2.  RE: Bad write-performance on iSCSI SAN

    Posted Aug 01, 2013 11:26 AM

    Only a thought: Did you already check whether the battery/write cache on the storage system is active and the LUNs are configured for write-back (rather than write-through) operation?


  • 3.  RE: Bad write-performance on iSCSI SAN

    Posted Aug 01, 2013 01:00 PM

    Thank you for your suggestion. As far as I can remember we had an issue with the battery. A restart of the SAN "fixed" this issue. (This was the solution provided by the third-party IT-Service)The SAN is configured for WRITE-THROUGH. I attached some screenshots, may you can help me solving this problem! Thank you so far!!

  • 4.  RE: Bad write-performance on iSCSI SAN

    Posted Aug 01, 2013 01:26 PM

    Unfortunately, I'm not familiar with this storage system. However, according to the documentation it should - by default - automatically switch to Write-Back caching if the battery is ok. It looks like you can override this setting in the "System Policy" tab, but I don't recommend doing this to avoid possible data loss!