Users Guide

Resiliency type Minimum number of
columns
Column-to-disk
correlation
Minimum number of
disks
Dual Parity 7 1:1 7
When sizing the column count of a VD, consider the following.
Will the VDs be
configured to
automatically
rebuild?
When a disk fails and an automatic rebuilds are enabled, the VD attempts to repair
the degraded VD by using existing free disk space in the pool. However, for an
automatic rebuild to occur, the VD must not only have free disk space, but also
have at least enough free disks available to restore the intended resiliency level
when also maintaining the original column count.
To account for this, the equations listed here for Two-way and Three-way mirrors
subtract 1 or 2 respectively for the column count calculation. If you do not intend
to enable automatic rebuilds for the VD subtracting is not necessary.
Is enclosure
awareness enabled
for the VD?
When enclosure awareness is enabled the data copies are spread across the
enclosures to allow for failure of a complete enclosure, when also maintaining
access to the data. Storage Spaces must have enough free disks to rebuild the VDs
in the remaining enclosures, when also maintaining the original column count.
NOTE: Results from the column count equations must be rounded down to the nearest whole
number. Also, any result where the column count is zero or less than zero indicates an invalid SSD
configuration for the pool. Add more SSDs to the pool to achieve a valid column count layout.
For Two-way mirror VDs:
Without enclosure awareness
With enclosure awareness
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