[CentOS-virt] Slightly OT: FakeRaid or Software Raid

Wed Dec 2 22:21:41 UTC 2009
Christopher G. Stach II <cgs at ldsys.net>

----- "Ben M." <centos at rivint.com> wrote:

> Thanks. The portability bonus is a big one. Just two other questions I
> think.
> - Raid1 entirely in dom0?

That's how I do it. dom0 should be handling the supply of the hardware services, and if dom0 has all of the drivers and physical disks under its control, it counts. dom0 should be able to handle the block scheduling better. Now, if booting guests with iSCSI disks and all the LUNs are on a SAN or otherwise networked and not directly under dom0 control, I would handle it differently.

Besides, you don't want the added complexity of managing all of the LVs and extra guest configuration.

> - Will RE type HDs be bad or good in this circumstance? I buy RE types
> but have recently become aware of the possibility where TLER 
> (Time-Limited Error Recovery) can be an issue when run outside of a 
> Raid, e.g. alone on desktop machine.

Definitely good as long as you have more than one disk in it. :) You want your disk to time out instead of holding up the array. You usually can't go wrong with NCQ and TLER. NCQ won't get you much in RAID 1, though. You can turn it off with the driver in most cases.

Christopher G. Stach II