On 10/01/12 8:39 PM, Keith Keller wrote:
> 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?
a server makes very little use of its system disks after its booted,
everything it needs ends up in cache pretty quickly. and you typically
don't reboot a server very often. why waste SSD for that?
I'd rather use SSD for something like LSI Logic's CacheCade v2 (but this
requires you use a LSI SAS raid card too)
> 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.)
I would suggest not using more than 10-11 disks in a single raid group
or the rebuild times get hellaciously long (11 x 3TB SAS2 RAID6 took 12
hours to rebuild when I ran tests). if this is for nearline bulk
storage, I'd use 2 disks as hot spares, and have 2 seperate RAID5 or 6
of 11 disks, then stripe those together so its raid 5+0 or 6+0. if
this is for higher performance storage, I would build mirrors and stripe
them (raid 1+0)
re: alignment, use the whole disks, without partitioning. then there's
no alignment issues. use a raid block size of like 32k. if you need
multiple file systems, put the whole mess into a single LVM vg, and
create your logical volumes in lvm.
--
john r pierce N 37, W 122
santa cruz ca mid-left coast
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