Raid Availability; Raid Availability Concept - Lenovo ThinkServer RD240 Software User's Manual

RAID
Level Capacity
5 RAID 5 provides redundancy for one drive failure without duplicating the contents of
entire drives. RAID 5 breaks up data into smaller blocks, calculates parity by performing
an exclusive-or on the blocks, then writes the blocks of data and parity to each drive in
the drive group. The size of each block is determined by the stripe size parameter,
which is set during the creation of the RAID set.
6 RAID 6 provides redundancy for two drive failures without duplicating the contents of
entire drives. However, it requires extra capacity because it uses two parity blocks per
stripe. This makes RAID 60 more expensive to implement.
00 RAID 00 (striping in a spanned drive group) involves partitioning each drive storage
space into stripes that can vary in size. The combined storage space is composed of
stripes from each drive. RAID 00 provides maximum storage capacity for a given set of
drives.
10 RAID 10 requires twice as many drives as all other RAID levels except RAID 1.
RAID 10 works well for medium-sized databases or any environment that requires a
higher degree of fault tolerance and moderate to medium capacity. Disk spanning
allows multiple drives to function like one big drive. Spanning overcomes lack of disk
space and simplifies storage management by combining existing resources or adding
relatively inexpensive resources.
50 RAID 50 requires two to four times as many parity drives as RAID 5. This RAID level
works best when used with data that requires medium to large capacity.
60 RAID 60 provides redundancy for two drive failures in each RAID set without duplicating
the contents of entire drives. However, it requires extra capacity because a RAID 60
virtual drive has to generate two sets of parity data for each write operation. This makes
RAID 60 more expensive to implement.
2.7

RAID Availability

2.7.1

RAID Availability Concept

2-32
Data availability without downtime is essential for many types of data
processing and storage systems. Businesses want to avoid the financial
costs and customer frustration associated with failed servers. RAID helps
you maintain data availability and avoid downtime for the servers that
provide that data. RAID offers several features, such as spare drives and
rebuilds, that you can use to fix any drive problems, while keeping the
servers running and data available. The following subsections describe
these features.
Introduction to RAID