[CentOS] new "large" fileserver config questions

Tue Oct 2 09:30:17 UTC 2012
John Doe <jdmls at yahoo.com>

From: Keith Keller <kkeller at wombat.san-francisco.ca.us>

> 1) The controller node has two 90GB SSDs that I plan to use as a
> bootable RAID1 system disk.  What is the preferred method for laying
> out the RAID array?

See the "Deployment Considerations" about SSDs and RAID:

> 2) With large arrays you often hear about "aligning the filesystem to
> the disk".  Is there a fairly standard way (I hope using only CentOS
> tools) of going about this?  Are the various mkfs tools smart enough to
> figure out how an array is aligned on its own, or is sysadmin
> intervention required on such large arrays?  (If it helps any, the disk
> array is backed by a 3ware 9750 controller.  I have not yet decided how
> many disks I will use in the array, if that influences the alignment.)

From memory:
For alignment, first partition starts at 2048.
For filesystem, call mkfs with appropriate -E stride=xxx,stripe-width=yyy
Stride = RAID Stripeisize_KB / FS blocksize_KB
Stripe-width = Stride * RAID_number_of_data_holding_disks (RAID6 = n-2 by example)