HP P2000 G3, Cli Reference Manual

Page: 139 / 532

HP P2000 G3 MSA System CLI Reference Guide 139
set cache-parameters
Description Sets a volume’s cache options.
NOTE: Only change the read-ahead cache settings if you fully understand how the host operating
system, application, and adapter move data so that you can adjust the settings accordingly. Be
prepared to monitor system performance and adjust read-ahead size until you find the optimal size
for your application.
Syntax
set cache-parameters
[write-policy write-back|write-through|wb|wt]
[optimization standard]
[read-ahead-size disabled|default|maximum|64KB|128KB|256KB|512KB|1MB|2MB|4MB
|8MB|16MB|32MB]
volume
Parameters
write-policy write-back|write-through|wb|wt
Optional. Sets the cache write policy, which determines when cached data is written to the disks.
The ability to hold data in cache while it is being written to disk can increase storage device speed
during sequential reads.
•
write-back
or
wb
: Write-back caching does not wait for data to be completely written to disk
before signaling the host that the write is complete. This is the default and preferred setting for a
fault-tolerant environment because it improves the performance of write operations and
throughput.
•
write-through
or
wt
: Write-through caching significantly impacts performance by waiting for
data to be completely written to disk before signaling the host that the write is complete. Use this
setting only when operating in an environment with low or no fault tolerance.
You can configure the write policy to automatically change from write-back to write-through when
certain environmental events occur, such as a fan failure. For details, see help for the set
auto-write-through-trigger command.
optimization standard
Optional. Sets the cache optimization mode:
•
standard
: Optimizes cache for both sequential and random reads. This is the default.
read-ahead-size
Optional. Controls the use and size of read-ahead cache. You can optimize a volume for sequential
reads or streaming data by changing the amount of data read in advance after two back-to-back
reads are made. Read ahead is triggered by two back-to-back accesses to consecutive logical block
address (LBA) ranges. Read ahead can be forward (that is, increasing LBAs) or reverse (that is,
decreasing LBAs). Increasing the read-ahead size can greatly improve performance for multiple
sequential read streams. However, increasing read-ahead size will likely decrease random read
performance.
•
disable
: Turns off read-ahead cache.
•
default
: Sets one chunk for the first access in a sequential read and one stripe for all
subsequent accesses. The controllers treat non-RAID and RAID-1 vdisks internally as if they have a
stripe size of 64 Kbyte, even though they are not striped. This setting works well for most
applications.
•
maximum
: Allows the controller to dynamically calculate the maximum read-ahead cache size for
the volume.
•
64 KB
,
128 KB
,
256 KB
,
512 KB
,
1 MB
,
2 MB
,
4 MB
,
8 MB
,
16 MB
, or
32 MB
: Sets a
specific cache size.