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Re: RAID for large disks

On Sat, 2008-06-07 at 17:05 -0400, Mag Gam wrote:
> Thanks for the responses all.
> I want RAID 5 but without mirroring. The data is important but not
> that important. 
> I am planning to use LVM.
> If the controller creates a stripe size of 16k, do I need to do
> anything special with physical extends (in pvcreate or vgcreate) ? 
> Do I need to do anything specific when creating a LV? I plan on
> striping my LV to create extra spindles. Do I need to create my ext3
> filesystem with any particular settings? I am looking for a optimal
> tuning guide with emphasis on performace versus redudancy.

If you use hardware raid, the bios of the box, the OS and all
applications will not be aware of any of the underlining RAID setup
parameters.  If you use two RAID5, your OS will only know it will have
sda and sdb.  On top of this you will put your file system (or lvm) and
none of these things will know anything about the hardware.  Nothing.
Not how many HDs you have, not what scsi bus they are on, not how fast
they are.  Not even that one of them dies (all though I have seen scsi
errors show up in /var/log/messages for one HD failure in a hdwr RAID,
go figure).  All you need to know at the level of the fs/LVM is you will
have two hd.  You can not have /boot on lvm (technically you can, but
not the version used by etch, lenny or sid) so you will need at least
one non-lvm partition.

Damon L. Chesser

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