On 03/28/2018 12:32 PM, Fred Cisin via cctalk wrote:
With very unreliable drives, that isn't acceptable. If each "drive"
within the RAID were itself a RAID, . . . Getting to be a complicated
controller, or cascading controllers, . . .
Many of the SCSI / SAS RAID controllers that I've worked with over the
last 10+ years have this cascading controller functionality. Most of
the RAID controlelrs that I've worked with would let you build a mirror
or stripe across some sort of underlying RAID. Typical examples are
striping (RAID 0) across mirrors (RAID 1) or multiple RAID 5 arrays.
'course not. Besides MTBF for calculating the probability of a second
drive failing within N hours, must also consider other factors, such as
external influences causing more than one drive to go, and the
essentially non-linear aspect of a failure rate curve.
You also need to take into account the additional I/O load imposed on
the remaining drives during a rebuild.
I usedto routinely run into software (Solstice Disk Suite?) RAID 1
mirrors on Solaris boxen for the OS (/) where different parts of each
drive would fail. So we'd end up with a situation where we had a decent
RAID, but we couldn't replace either disk. This usually involved taking
an entire backup of the machine, replacing both disks, and restoring the
data.
--
Grant. . . .
unix || die
