Array configuration guidelines for storage systems

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 number 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 disk (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:
  1. For optimal performance, use arrays with between 6 and 8 member disks.
  2. When creating arrays with mirroring, the number of component disks in each array does not affect redundancy or performance.