Meta Cache Distribution; Figure 87 Meta Cache Distribution - Fujitsu ETERNUS DX S5 Series Design Manual

4. NAS Functions
NAS System (NAS Volume Management)
SDVs and SDPVs cannot be created in a TPP. SDVs are automatically created in the RAID group that is specified
when setting snapshot. SDPVs must be created separately. When acquiring 128 generations of snapshots, a
RAID group for registering an SDV and a RAID group for registering an SDPV must be prepared separately.

Meta Cache Distribution

The meta cache distribution function is used to balance the file system management data (or meta cache) that
is concentrated in one controller due to problems such as a NAS volume error.
When NAS volumes are created, the meta cache is deployed in the cache memory of the controller for each NAS
volume. Meta cache is distributed to either CM#0 or CM#1 for each NAS volume so that the meta cache is
balanced in both controllers.
If an error occurs in the NAS volume during an operation, a failover of the meta cache to the other controller is
performed. The cache memory capacity in one controller becomes insufficient and the performance may be
reduced if the operation continues in this condition.
Figure 87 Meta Cache Distribution
State where the meta cache is distributed to both CMs in a balanced manner (initial deployment)
Meta cache
Meta cache failover
occurs
State where the meta cache is unbalanced due to problems such as errors detected in the NAS volume
Meta cache
Your maintenance engineer may ask you to execute the meta cache distribution function during maintenance.
The target volumes for the meta cache distribution function are NAS user volumes and NAS backup volumes. In
addition, the meta cache distribution function can be performed automatically and manually. Automatic meta
cache distribution is disabled by default.
CM#0
Meta cache
NAS volumes
ETERNUS DX
CM#0
Meta cache
NAS volumes
ETERNUS DX
CM#1
Meta cache
Meta cache
Meta cache is distributed
CM#1
Meta cache
Meta cache
Meta cache
168 Design Guide