System information

95 of 114Release 7.0VNX™ System Operations
Allocation of LUNs
• The RAID group containing the VNX for file control LUNs must be
dedicated to NAS. No SAN LUNs might reside on this RAID group.
LUN numbers 0 to 15 are dedicated to VNX for file control LUNs.
Note: Any attempt to allocate storage in a LUN number between 0-15
will result in Error 3147: volume <disk-id> resides on a
reserved disk. If a reserved disk is already used in an AVM storage
pool, no additional storage will be allocated from the volume built on the
reserved disk. This restriction affects only new space allocation.
Existing file systems will continue to function normally. If you see this
error, contact your EMC Customer Support representative so corrective
action can be taken.
• All other RAID groups are not restricted to all SAN or all NAS. The
RAID group can be sliced up into LUNs and distributed to either a
SAN or NAS environment.
• RAID groups do not have to be split into two, four, or eight equal-size
NAS LUNs, but they must be balanced across the array. This means
an equal number of same-size NAS LUNs must be spread across
storage processor (SP) A and SP B.
Note: If you do not configure the LUNs across SP A and SP B properly,
you will not be able to manage the LUNs by using the Unisphere
software.
Array read/write cache
settings
For the VNX for file with a VNX for block integrated array, set the read or
write caches with the following principle: the rule of the thumb is to
allocate one third of memory for read cache and two thirds for write
cache (remember that read cache is for prefetch and that if data is in the
write cache, it is read from cache, not from disk).
For example:
• CX array with 2 GB of memory per SP:
read cache = 32 MB, write cache = 1465 MB
• CX array with 4 GB of memory per SP:
read cache = 146 MB, write cache = 3072 MB
• FC4700-2 array:
read cache = 32 MB, write cache = 805 MB
Note: For gateway servers, write cache is required. The VNX for block
documentation provides more details on settings.
Table 10 VNX for file/VNX for block NAS and SAN environment considerations (page 2 of 3)
Category Considerations