2 Replies Latest reply on Jun 27, 2012 9:31 PM by Xavier

    RAID 5 Extremly slow write speed!?


      Hi everyone!


      I was hoping that some one can help me out here, I have a z77mobo and I am using the iRST to create a raid 5 array using 5 2TB drives, 3 seagates and 2 WD.


      the problem I have is that once the array is created and initialized, the write speeds are really slow, down to 12MB/s to 20MB/s.


      Is this normal?


      I am using IRST V11.1.0.1106


      clean install of win 7.


      The wierd thing is that I was using this same array(same disks) on a z68 mobo and had better write speeds, in the 110MB/s ball park.


      Any comments or suggestions on this would be greatly appreciated!!

        • 1. Re: RAID 5 Extremly slow write speed!?


          1) if you have a UPS backup, you should -> Computer Management->Device Manager->Disk Drives. Bring up the property page for your raid disk and select Policies. Make sure that both Enable write-caching is on and also select "Turn off Windows write-cache buffer flushing on the device". Without buffer flushing you should see performance ~200-250MB/sec. With buffer flushing you are probably writing slower than a single drive. Windows will flush everything when you do a shutdown. Also, see the Windows Sysinternals package for a command to "sync" a device.


          The reason for the UPS is that you need a means to protect your disk data (including raid metadata) from being lost. If your system has other reliability issues that cause system crashes, you should let Windows flush its write-cache buffer. Also, you might not need an expensive UPS, but be aware that cheap UPS's can be the flakiest device that you can plugin. There's nothing more disconcerting to me than to see a UPS quit even when there is line power.


          2) 110MB/sec is not very good either. You might check the other machine's buffer flush settings.


          3) You are likely losing some performance because your raid disk drives aren't all the same model. Even though the consumer description may say 7200RPM, 16MB disk cache and SATA-2, there are different access times and effective transfer rates from model to model and from vendor to vendor. You will likely find that one vendor's drives perform better/worse in this setting.


          Oh yes, don't use the so-called "green" drives for raid-5 and make sure your setup BIOS is configured to power up drives with a ~2 sec delay. You'll wind up watching a disk get reconstructed when a drive drops out of the raid configuration.



          • 2. Re: RAID 5 Extremly slow write speed!?



            I have tried the settings that you mentioned above but I am still getting the same speed. This could be to the fact that the array is"initializing", about 20%, I will try again in a few days as this takes 3 days or so to reach 100%. I suspect that the initializing is keeping the HDDs busy.... I will post my result then...