Author Topic: RAID over File System (RAID-F) and parity disk(s) requirements...  (Read 2494 times)

Offline Brahim

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 8,547
  • Karma: +204/-16
    • View Profile
RAID over File System (RAID-F) and parity disk(s) requirements...
« on: September 26, 2014, 09:41:48 am »
RAID over File System (RAID-F) and parity disk(s) requirements

I have recently been informed that some users are still having confusion in regard to parity space requirement when using RAID-F.

It is important to understand that RAID-F does not care about the size of your disks. All it cares about are used data space and available parity space.
Many users sometimes get confused as to why they have out of parity space error or other anomalies even though they are using disk of the same size.

Please note the followings:
  • The available usable disk space vary per manufacturers even for the same advertised disk capacity.
  • Even when disks are of the same make and model, the available disk space will vary based reallocated sector count and space occupied by file system metadata
  • RAID-F use a few MBs off the parity disk(s) for metadata information storage

To address these aspect, the Storage Pool has a "Reserve" property to ensure that no DRU over fills.
When starting with disk with existing data, you should make sure that no disk is filled to the brim as that will likely create issue.

So, pay attention to your DRUs and move data off overfilled DRUs.
The next major release of RAID-F will likely have an automated process to handle this transparently. However, keep these aspect in mind till then.