1 Reply Latest reply on Mar 19, 2013 10:21 AM by john_s@intel

    I have a question about performance of the  Integrated RAID Module RMS25CB080

    michaelww

      I have a question about performance of the RAID controller Integrated RAID Module RMS25CB080

      I have built RAID 5 array on 7 discs seagate Cheetah 15K.7 ST3300657SS

      With  settings (Write-back caching) it shows very good performance and with settings (Write-throught caching) it shows very poor performance on writing (twice worse).

       

      RAID BIOS - Firmware Paskage Version  23.9.0-0018

      HDD -  Type: Cheetah 15K.7 ST3300657SS  FW:  0008

      RAID Cache Disabled:

           Strip Size: 256k

           Write Policy: Write Through

           Read Policy:  No Read Ahead

           IO Policy: Direct IO

           Disk Cache Policy: Disable

      RAID Cache Enabled:

          Strip Size: 256k

          Write Policy: Write Back with BBU

          Read Policy:  Read Ahead

          IO Policy: Direct IO

          Disk Cache Policy: No Change

      In case (RAID Cache disabled) write speed  decreased  in  twice time(random and sequential). OS CentOS 6.3

      I used FIO and simple copy (dd and cp).  

      The log files registered by IOStat and gnuplot built graphs by use this logs.

      Graphs are attached.

      GdiskWriteWithCache.pngdiskWriteWithoutCache.png

       

      Must it be this way or is it a bug?

        • 1. Re: I have a question about performance of the  Integrated RAID Module RMS25CB080
          john_s@intel

          Michael,

           

          RAID 5 uses block-level striping with parity data distributed across all member disks. RAID 5 can suffer from somewhat lesser write performance because parity must be updated on each write. This is because parity must be calculated on each write, requiring read-modify-write sequences for both the data block and the parity block.

           

          When comparing write-through and write-back cache settings, write-back caching yields better performance than write-through caching because it reduces the number of write operations to main memory.

           

          With write-through, the write is done to both the cache and to disks at the same time. Write-through mode means that the cache is only used as a buffer and the drive will immediately write data the operating system instructs it to. The operating system sends a command to the drive and the operating system is forced to wait while the drive completes the write.

           

          With write-back, the write is done to the cache. The write to the disks is delayed until the cache containing the data are about to be modified/replaced by new content. Write back will cache data to be written and only write it when the drive is idle. The operating system does not need to wait for the drive to actually finish writing the data.

           

          Regards,

          John