HP StorageWorks Command View SDM Installation and User Guide (T1086-96023, February 2005)

Command Line User Interface 169
Command Line User Interface
RAID 1+0 Writes in Place OPAQUE The number of write operations to previously written LUN
addresses posted out of the write cache to RAID 1+0
storage.
Usage
Rewrites are host writes to LUN addresses that have
already been written at least once since the LUN was
created. AutoRAID will decide whether to place write data
into RAID 1+0 or RAID 5 DP storage when it is posted out
of the write cache. When RAID 1+0 is the destination for a
rewrite, it will be performed by updating the data in place
rather than relocating the cluster containing the data. This
provides the performance benefit of AutoRAID for random
writes by keeping the write working set in RAID 1+0
storage. Random write performance will be optimized
when the majority of random writes occur as RAID 1+0
writes in place.
RAID 5 DP Allocation (absolute) LUN The number of logical blocks in the LUN that are stored
using the RAID 5 DP storage method.
Usage
RAID 5 DP provides better storage efficiency than RAID
1+0 and approximately equivalent sequential write
performance. AutoRAID will attempt to detect a sequential
write workload and store the data in RAID 5 DP to get
better storage efficiency. As the array becomes filled with
data AutoRAID will migrate more of the data to RAID 5
DP. AutoRAID preserves a minimum of 10% of the data in
RAID 1+0 when the array is completely full. This metric
combined with the RAID 1+0 Allocation metric for a LUN
will indicate the class of random write performance that
can be expected from the LUN. If the LUN does not
contain much of the write working set, the data in the LUN
may be almost completely stored as RAID 5 DP.
Table 12 Performance Metrics (Continued)
Metric Categories Description/Usage