Dell Perc 5/i Performance issues

Scott Long scottl at
Sun Jun 20 18:50:07 UTC 2010

I just set up a machine with the following GPT scheme:

=>        34  5853511613  mfid0  GPT  (2.7T)
          34         128      1  freebsd-boot  (64K)
         162         862         - free -  (431K)
        1024     2097152      2  freebsd-ufs  (1.0G)
     2098176     4194304      3  freebsd-swap  (2.0G)
     6292480     2097152      4  freebsd-ufs  (1.0G)
     8389632   104857600      5  freebsd-ufs  (50G)
   113247232  5740264414      6  freebsd-ufs  (2.7T)
  5853511646           1         - free -  (512B)

After the first partition, I created a deliberate gap for alignment, reflected in the second line.  The third line shows a starting offset of sector 1024, which is 512KB.  This should be a good generic start point for most RAID geometries with a stripe size <= 512KB.  The rest are normal /, swap, /var, /usr and /opt partitions.  The single free sector on the final line is probably a calculation error on my part, there's no particular reason for it.

The gpart man page has good descriptions on how to create partitions and make the GPT scheme bootable.  It's not very automated, you'll need to have a calculator handy, but it works.


On Jun 20, 2010, at 12:20 PM, Steven Hartland wrote:

> Does anyone know of a nice how to guide for achieving this?
> ----- Original Message ----- From: "Scott Long" <scottl at>
> 2. Partition alignment.  If you're using classic MBR slices, everything gets misaligned by 63 sectors, making it impossible for the controller to optimize both reads and writes.  If the array is used for secondary storage, simply don't use an MBR scheme.  If it's used for primary storage, try using GPT instead and setting up your partitions so that they are aligned to large power-of-2 boundaries.
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