IBM System Storage DS4000, Руководство по оборудованию

Страница: 127 / 566

Chapter 4. IBM System Storage DS planning and configuration
109
The recommendations for using RAID 10 are as follows:
򐂰 Use RAID 10 whenever the array experiences more than 10% writes. RAID 5 does not
perform as well as RAID 10 with a large number of writes.
򐂰
Use RAID 10 when performance is critical. Use write caching on RAID 10. Because a
RAID 10 write will not be completed until both writes have been done, write performance
can be improved through the use of a write cache (be sure it is battery-backed up).
When comparing RAID 10 to RAID 5:
򐂰 RAID 10 writes a single block through two writes. RAID 5 requires two reads (read original
data and parity) and two writes. Random writes are significantly faster on RAID 10.
򐂰 RAID 10 rebuilds take less time than RAID 5 rebuilds. If a real disk fails, RAID 10 rebuilds
it by copying all the data on the mirrored disk to a spare. RAID 5 rebuilds a failed disk by
merging the contents of the surviving disks in an array and writing the result to a spare.
RAID 10 is the best fault-tolerant solution in terms of protection and performance, but it
comes at a cost. You must purchase twice the number of disks that are necessary with RAID
0.
The following note and Table 4-2 summarize this information.
Table 4-2 RAID levels comparison
Summary: Based on the respective level, RAID offers the following performance results:
򐂰 RAID 0 offers high performance, but does not provide any data redundancy.
򐂰
RAID 1 offers high performance for write-intensive applications.
򐂰 RAID 3 is good for large data transfers in applications, such as multimedia or medical
imaging, that write and read large sequential chunks of data.
򐂰 RAID 5 is good for multi-user environments, such as database or file system storage,
where the typical I/O size is small, and there is a high proportion of read activity.
򐂰 RAID 6 offers high availability with performance slightly lower than RAID 5.
򐂰 RAID 10 offers higher performance than RAID 1 and more reliability than RAID 5 and is
the best option for random write performance.
RAID Description Application Advantage Disadvantage
0 Stripes data across
multiple drives. IOPS
Mbps Performance, due to
parallel operation of the
access. No redundancy. If one
drive fails, the data is
lost.
1 The disk's data is
mirrored to another
drive. IOPS Performance, as
multiple requests can
be fulfilled
simultaneously. Storage costs are
doubled.
10 Data is striped across
multiple drives and
mirrored to the same
number of disks. IOPS Performance, as
multiple requests can
be fulfilled
simultaneously.
This is the best option
for random write
performance.
Most reliable RAID
level. Storage costs are
doubled.