linux-kernel - How do I tell if my partition is aligned for a 64k/RAID-6?

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Date:	Thu, 25 Dec 2008 08:31:18 -0500 (EST)
From:	Justin Piszcz <jpiszcz@...idpixels.com>
To:	linux-kernel@...r.kernel.org
cc:	linux-raid@...r.kernel.org, bug-parted@....org,
	ataraid-list@...hat.com, xfs@....sgi.com
Subject: How do I tell if my partition is aligned for a 64k/RAID-6?

Output:

===============================================================================

p34:~# parted /dev/sda print unit s print unit chs print
Model: AMCC 9650SE-16M DISK (scsi)
Disk /dev/sda: 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

Model: AMCC 9650SE-16M DISK (scsi)
Disk /dev/sda: 25390350336s
Sector size (logical/physical): 512B/512B
Partition Table: gpt

Number  Start  End           Size          File system  Name  Flags
  1      34s    25390350302s  25390350269s  xfs

Model: AMCC 9650SE-16M DISK (scsi)
Disk /dev/sda: 1580476,53,56
Sector size (logical/physical): 512B/512B
BIOS cylinder,head,sector geometry: 1580476,255,63.  Each cylinder is 8225kB.
Partition Table: gpt

Number  Start   End            File system  Name  Flags
  1      0,0,34  1580476,53,23  xfs

p34:~#

===============================================================================

I created a partition from 0Gb to 13T on the following LUN, but how do I 
verify this is aligned to the (hardware) 64KiB raid-6 array?

Unit  UnitType  Status         %RCmpl  %V/I/M  Stripe  Size(GB)  Cache  AVrfy
------------------------------------------------------------------------------
u0    RAID-6    OK             -       -       64K     12107.1   ON     ON

===============================================================================

p34:~# xfs_info /dev/sda1
meta-data=/dev/sda1              isize=256    agcount=12, agsize=268435455 
blks
          =                       sectsz=512   attr=2
data     =                       bsize=4096   blocks=3173793783, imaxpct=5
          =                       sunit=0      swidth=0 blks
naming   =version 2              bsize=4096
log      =internal               bsize=4096   blocks=32768, version=2
          =                       sectsz=512   sunit=0 blks, lazy-count=0
realtime =none                   extsz=4096   blocks=0, rtextents=0

===============================================================================

I am not worried about the filesystem as the defaults usually get it right 
but with parted, this is the first time I had to use it for home use and 
with RAID-6 I am noticing slower performance with 15 disks (1 is a spare) 
in RAID-6 (albeit slower 7200 ones, RE3s) than I was getting with 10 
raptor150s in RAID-6 (but I had used fdisk there).

Justin.

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