[Gllug] Hardware RAID On-Disc Format

[Bruce Richardson]

On Mon, Mar 15, 2004 at 01:06:39PM +0000, Doug wrote:
> So these disks really might have data written in an undocumented
> proprietary format on them?

Well, consider that most RAID levels include having data "striped"
across multiple disks.  The physical hard disks used in this manner
don't really have filesystems.  Any recognisable filesystems have been
created on the virtual disks, not the physical disks.  How did you
expect to recover a file from one disk out of (say) a RAID 5
configuration, given that not only the file but the filesystem is only
partially present?

The standards for RAID controllers describe the controller interface and
the general RAID mechanisms: they don't dictate precisely how the
individual disks should be controlled.

Backups are your only protection from a controller failure.  However,
RAID can make it very easy to recover from a disk failure.  This
morning we discovered that one of the disks in one of our Dell rack
servers had failed.  It was part of a RAID 5 array, so the box was still
functioning with no loss of data (just beeping annoyingly).  Pulled the
faulty drive out, slapped a new one in, rebuilt the array, all without
so much as a reboot.

-- 
Bruce

Hierophant: someone who remembers, when you are on the way down,
everything you did to them on the way up.
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