Avago Technologies 3ware SAS 9750-16i4e - Manual (Page 110)

Chapter 7. Configuring Units
98 3ware SATA+SAS RAID Controller Card Software User Guide, Version 10.2
In order to replace a failed drive, a hot spare must have the same or larger
storage capacity than the drive it is replacing, and must be of the same type
(SAS or SATA).
The Auto-Rebuild policy allows automatic rebuilding to occur with available
drives that are not designated as spares. For more information, see “Setting
the Auto-Rebuild Policy” on page 71.
Specifying a Hot Spare through 3DM2
If you need to add a drive to be used as the hot spare, follow the instructions
under “Adding a Drive” on page 129.
To specify a hot spare
1 In 3DM2, choose Management >> Maintenance.
2 In the Available Drives list, select the drive you want as a hot spare by
marking the checkbox in front of its Port number.
3 Click Set Spares .
You will see the status change to OK-SPARE .
Specifying a Hot Spare through 3BM
1 On the main 3BM screen, in the list of Available Drives , highlight the
drive you want to use.
2 Type s to specify that the selected drive will be the hot spare.
You’ll see the words “Hot Spare” appear next to the drive in the Available
Drives list.
Note: 3ware’s 9750 RAID controllers use drive coercion so that drives from
differing manufacturers and with slightly different capacities are more likely to be
able to be used as spares for each other. Drive coercion slightly decreases the
usable capacity of a drive that is used in redundant units.
The capacity used for each drive is rounded down to the nearest GB for drives
under 45 GB (45,000,000,000 bytes), and rounded down to the nearest 5 GBytes
for drives over 45 GB. For example, a 44.3 GB drive will be rounded down to 44
GBytes, and a 123 GB drive will be rounded down to 120 GBytes.
If you have 120 GB drives from different manufacturers, chances are that the
capacity varies slightly. For example, one drive might be 122 GB, and the other 123
GB, even though both are sold and marketed as “120 GB drives.” 3ware drive
coercion uses the same capacity for both of these drives so that one could replace
the other.