Four (4) Volume Per Physical Disk Limitation in WHS

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Just as a note to anyone running multiple large disks in Raid 6 for Windows Home Server. I was setting up new Raid 6 arrays on the WHS this weekend, controlled by an Adaptec 31605 and was greeted by a nice error message. WHS is limited to four volumes per physical drive using basic discs. A quick search of the Adaptec site showed the problem and a proposed fix, dynamic disks. While this would be great under normal circumstances, WHS does not play well with dynamic disks.

Practically speaking, instialling Windows Home Server limits your arrays stemming from a disk to 8TB (2TB for non-GPT * 4 volumes =  8TB). As larger drives are used, the net effect is fewer drives can be utilized in RAID. Practically speaking with 2TB drives, one hits this wall at:

  • 5x 2TB disks in raid 5
  • 6x 2TB disks in raid 6
  • 8x 2TB disks in raid 10

When setting up a WHS using RAID, remember these limits! As an astute reader will likely note, 2TB drives do not correlate to 2TB in usable capacity, so in theory one could use an additional disk in the above example to make exactly 8TB of storage available.

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