With virtualization, ensure that the storage devices are
configured to provide some type of redundancy against hard disk failures.
A failure of a storage
device can affect
a larger amount of storage that is presented to the hosts. To provide
redundancy, storage devices can be configured as arrays that use either
mirroring or parity to protect against single failures.
When creating arrays with parity protection (for example, RAID-5 arrays), consider how many
component disks you want to use in each array. If you use a large amount of disks, you can reduce
the number of disks that are required to provide availability for the same total capacity (1 per
array). However, more disks mean that it takes a longer time to rebuild a replacement disk after a
disk failure, and during this period a second disk failure causes a loss of all array data. More
data is affected by a disk failure for a larger number of member disks because performance is
reduced while you rebuild onto a hot spare (a redundant disk) and more data is exposed if a second
disk fails before the rebuild operation is complete. The smaller the number of disks, the more
likely it is that write operations span an entire stripe (stripe size, multiplied by the number of
members, minus one). In this case, write performance is improved. The number of disk drives required
to provide availability can be unacceptable if arrays are too small.
Notes: - For optimal performance, use arrays with between 6 and 8 member disks.
- When creating arrays with mirroring, the number of component disks in each array does not affect
redundancy or performance.