The (up to) 30% percent figure is mentioned here:

This user writes about the problem:
XP, and virtually every O/S and partitioning software of XP's day, by default 
places the first partition on a disk at sector 63. Being an odd number, and 
31.5KB into the drive, it isn't ever going to align with any stripe size. This 
is an unfortunate industry standard.
Vista on the other hand, aligns the first partition on sector 2048 by default 
as a by-product of it's revisions to support large-sector sized hard drives. As 
RAID5 arrays in write mode mimick the performance characteristics of 
large-sector size hard drives, this comes as a great if not inadvertent 
benefit. 2048 is evenly divisible by 2 and 4 (allowing for 3 and 5 drive arrays 
optimally) and virtually every stripe size in common use. If you are however 
using a 4-drive RAID5, you're SOOL.

Page 9 in this PDF (EMC_BestPractice_R22.pdf) shows the problem graphically:


Now to my setup / question:

# fdisk -l /dev/sdc

Disk /dev/sdc: 150.0 GB, 150039945216 bytes
255 heads, 63 sectors/track, 18241 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x5667c24a

   Device Boot      Start         End      Blocks   Id  System
/dev/sdc1               1       18241   146520801   fd  Linux raid autodetect


If I use 10-disk RAID5 with 1024 KiB stripe, what would be the correct start and end size if I wanted to make sure the RAID5 was stripe aligned?

Or is there a better way to do this, does parted handle this situation better?

What is the best (and correct) way to calculate stripe-alignment on the RAID5 device itself?


The EMC paper recommends:

Disk partition adjustment for Linux systems
In Linux, align the partition table before data is written to the LUN, as the partition map will be rewritten and all data on the LUN destroyed. In the following example, the LUN is mapped to /dev/emcpowerah, and the LUN stripe element size is 128 blocks. Arguments for the fdisk utility are
as follows:
fdisk    /dev/emcpowerah
x      # expert mode
b      # adjust starting block number
1      # choose partition 1
128 #    set it to 128, our stripe element size
w      # write the new partition


Does this also apply to Linux/SW RAID5? Or are there any caveats that are not taken into account since it is based in SW vs. HW?


What it currently looks like:

Command (m for help): x

Expert command (m for help): p

Disk /dev/sdc: 255 heads, 63 sectors, 18241 cylinders

Nr AF  Hd Sec  Cyl  Hd Sec  Cyl     Start      Size ID
 1 00   1   1    0 254  63 1023         63  293041602 fd
 2 00   0   0    0   0   0    0          0          0 00
 3 00   0   0    0   0   0    0          0          0 00
 4 00   0   0    0   0   0    0          0          0 00

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