User Manual
BC4000 Series RAID Controllers
02/13/06
B ro ad c om C o r p or at i on
Document
BC4000-UM100-R
Working with Spares
Page 47
W
ORKING
WITH
S
PARES
A
BOUT
S
PARING
O
PTIONS
The BC4000 Series RAID controller supports three sparing options.
Spares are restored in the following order:
•
Dedicated
•
Distributed
•
Global
U
SING
D
ISTRIBUTED
S
PARING
RAIDCore’s proprietary distributed sparing feature reserves space on each drive in an array. This space is
used when the data from a failed drive is being regenerated during a restore task. Whereas other methods of
sparing (such as dedicated spares) provide the same level of protection, distributed sparing provides better
performance because all drives are active in an array and are not sitting idle, as is the case with dedicated
spares. Another advantage of distributed spares is that because all drives are active, a drive cannot fail and
go unnoticed, as is the case with dedicated or global spares. This is because with distributed sparing, each
array has its own dedicated fail-over spaces. This averts the potential problem of having insufficient space to
start a fail-over on the single disk that has been assigned as a spare.
A distributed spare is assigned at the time an array is created or transformed. Distributed spares are valid only
for RAID5 (four or more drives), RAID50 (four or more drives per RAID5 set), and RAID10 and RAID10n (six
or more drives).
This spare type is the most protective because space is allocated when the array is created. Like a dedicated
spare, this spare type is assigned to a specific array. If you initially created an array without a distributed spare,
you must transform the array to add a distributed spare. This is because a distributed spare can be assigned
only when an array is being created or transformed.
Distributed
A patent-pending sparing option that consists of reserved space on
each disk in an array
Dedicated
A spare disk assigned to a specific, redundant array
Global
A spare disk that is shared by multiple arrays
Notes:
•
An array is marked critical or offline if a disk returns failure to an I/O, or if the SATA or power cable
is disconnected.
•
You can assign one or more spares to a redundant array type.
•
Spare assignments do not apply to non-redundant array types. To protect this data, you must first
transform the array to a redundant array type (see
“Transforming Arrays” on page 84
). You can
then assign spares.
