Redundant NFS storage setup (part 3) : The disappointingPERC5/E(solved?)

[Matthias Saou]

Harald_Jensas at dell.com wrote :

> Kevin, Did you ever try to create your Hardware RAID striped partitions aligned? 
> This will cause less stripe crossings and thus less parity to calculate for RAID 5 writes. It should also improve read performance.
> 
> In this article they report up to 30% performance increase, in their tests, with properly aligned partitions.
> http://insights.oetiker.ch/linux/raidoptimization.html
> 
> Assuming block size is 512 bytes.
> If Stripe Size is (64KB/512 byte = 128 Blocks) align the partition to block 128.
> If Stripe Size is (128KB/512 byte = 256 Blocks) align the partition to block 256.
> 
> 1. Enter fdisk /dev/sd<x> where <x> is the device suffix.
> 2. Determine if any partitions already exist.
> 3. Type n to create a new partition.
> 4. Type p to create a primary partition.
> 5. Type 1 to create partition No. 1.
> 6. Select the defaults to use the complete disk.
> 7. Type t to set the partition's system ID.
> 8. Type in the code for the partition type you want.
> 9. Type x to go into expert mode.
> 10. Type b to adjust the starting block number.
> 11. Type 1 to choose partition 1.
> 12. Type 128 to set it to 128 (the array's stripe element size).
> 13. Type w to write label and partition information to disk.

This is quite interesting, but I'm a little confused as to how to
achieve this when using a gpt partition table.

Here's what parted shows me :

Model: DELL PERC 5/E Adapter (scsi)
Disk /dev/sdb: 13.0TB
Sector size (logical/physical): 512B/512B
Partition Table: gpt

Number  Start   End     Size    File system  Name  Flags
 1      17.4kB  13.0TB  13.0TB  xfs          MD1        

The partition was created with "mkpart MD1 0 100%", and I don't see how
to access any "expert" features with parted. Here's what fdisk shows
me (FWIW, since it doesn't support gpt) :

Disk /dev/sdb: 12995.4 GB, 12995497295872 bytes
255 heads, 63 sectors/track, 1579945 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1               1      267350  2147483647+  ee  EFI GPT

As you can see, I have the "63 sectors/track" value which the article
considers sub-optimal. Is there any way to change this?

Another thing I'll try is to use LVM on the block device directly,
basically replacing the partition, an see how that performs.

Matthias

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