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v Defining large volumes may take several minutes to complete. An IBM
v The maximum number of volumes on a system is 128. The maximum number of
v Multiple blade servers can be mapped to a single volume if clustering is
v Mapping a single volume to multiple blade servers can be done using the
Understanding RAID levels
This topic details RAID level characteristics as they relate to the IBM BladeCenter S
SAS RAID Controller Module.
A Redundant Arrays of Independent Disks (RAID) is a collection of two or more
disk drives that present an image of one or more logical disk drives. In the event
of a disk failure, the data can be read or regenerated from the other disk drives in
the array due to data redundancy. There are several considerations in deciding
which RAID level to choose for your configuration: the amount of storage you
have at your disposal, cost, and security requirements.
The IBM BladeCenter S SAS RAID Controller Module supports the following RAID
levels:
RAID 0 uses a process called striping, which is the splitting of data across more
than one disk. A RAID 0 configuration adds no redundancy and the loss of any
one disk in a stripe causes the failure of all the disks in that stripe.
RAID 1 uses a process called mirroring. In a RAID 1 configuration, all of the data
on a disk is replicated onto a second peer-level disk. If one of the disks in the pair
fails, the other continues running unaffected. RAID 1 requires a two-disk
configuration.
RAID 5 uses a process called striped parity. This process writes data and parity
information in stripes along three or more drives. If a drive in the array fails, you
do have to replace it, but the array is not destroyed by a single drive failure. If a
drive failure occurs, subsequent reads are calculated from the distributed parity.
The first predefined configuration file (CannedConfig_RSSM.cfg) sets up a RAID 5
array using six available drives. RAID 5 requires a minimum 3 disk configuration.
RAID 10 uses a process called striping across mirrors. This process requires a set of
even numbered disks, with four disks being the minimum number required. The
36
IBM SAS RAID Controller Module: Installation and User's Guide IBM BladeCenter S SAS RAID Controller Module
BladeCenter S takes approximately 10 minutes to define an 11 TB volume, and
may take longer if the system is performing other tasks.
volumes on a host is 16.
configured. See "Configuring blades for Microsoft Cluster Service" on page 40
for more information.
hostlun command through the RAID Controller command line interface. See
"hostlun" on page 85 for more information.
Table 5. RAID levels and characteristics
RAID levels
Characteristics
0
Striping
1
Mirroring
5
Striping with Distributed Parity
10
Striping across mirrors
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Troubleshooting
