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RAID-5 / RAID-4 Can be Partitioned to Suit

Last updated 2014-06-08 - Send Feedback
Related: backup, RAID, RAID-1, RAID-4, RAID-5, SoftRAID, storage, Thunderbolt, video

A RAID-5 or RAID-4* setup is not restricted to one huge volume; it’s perfectly fine to create more than one volume to suit one’s needs. SoftRAID makes it trivial to create such partitions regardless of the type of RAID (or non-RAID).

* RAID-4 offers the same fault tolerance characteristics as RAID-5, but sometimes has better performance.

Three 5TB RAID-5 volumes using four 5TB drives

As shown below, four 5TB drives in an OWC Thunderbay enclosure have been used to create three 5TB volumes instead of one 15TB single volume: Master, Archive1, Archive2. It could just as well have been 4TB each. This approach can serve important goals:

  • The first partition will be the fastest one, thus guaranteeing high speed.
  • All partitions will be MUCH faster tha a single drive / single volume or RAID-1 mirror approach.
  • Partition size can be matched to the capacity of external backup drives, e.g. for cloning as a backup strategy.
  • Explicit and unambiguous organization of files for backup and search, e.g. Master for more recent work with Archive1 and Archive2 for older material for faster and more targeted backup, as well as optimizing speed for current work (volume Master being fastest).

While not necessarily sensible, one could have made a RAID-5 for Master, a RAID-1+0 for Archive1, and a RAID-1 mirror for Archive2! There is no restriction on the flexibility.

Taking the 3-partition case, when a drive should fail, all three partions will be protected but running in “Degraded” state. Replacing the failed drive will rebuild all in turn. Compare that to a single-drive setup (slower and loss of volume), RAID-1 mirror (slower but no more fault tolerance), or RAID-0 stripe (slightly fasterm but loss of volume). The partitioned setup

Three 5TB RAID-5 volumes using four 5TB drives
Three 5TB RAID-5 volumes using four 5TB drives

Performance implications

Shown below are the three partitions. The fastest partition (green + red lines) is indeed much faster than the slowest partition (yellow + purple), but only modestly faster than the middle partition.

RAID-5 performance using three 5TB volumes on the same four 5TB drives

MacPerformanceGuide.com
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