LSI RAID Controller Cache Settings

Force LSI controller to flush cache to disk.
MegaCLI –AdpCacheFlush -aALL
This option sends the contents of cache memory to the virtual disk(s). If the MegaRAID system must be powered down rapidly,
you must flush the contents of the cache memory to preserve data integrity.

Direct IO, not Cached IO
The LSI slidedeck MegaRAID Performance Tuning and Benchmark Tips states that Direct IO is the correct setting on RAID controllers. "All read data is transferred directly to host memory, bypassing RAID controller cache. Any Read Ahead data is cached. All write data is transferred directly from host memory bypassing RAID controller cache if Write-Through cache is set.

"The Cached IO" (All read and write data passes through controller cache memory on its ways to or from host memory, includes write data in Write-Through mode), legacy option is being eliminated in a future release.

Disk Cache Policy
Disk Cache Policy determines whether the physical hard-drive write cache is enabled or disabled. When Write Policy is set to Write Thru mode, Disk Cache Policy can have very big impact on write performance. When Write Policy is set to Write Back mode, impact of Disk Cache Policy is much smaller and in many cases negligible.
When Disk Cache Policy is enabled, there is a risk of losing data in the hard drive cache if a power failure occurs. The data loss may be fatal and may require restoring the data from a backup device.

Write Policy: Write-Back (ONLY IF BBU is present)
With the write-back caching strategy, a completion status is sent to the host operating system as soon as data is written to the RAID cache. Data is written to the disk when it is forced out of the controller cache memory. Write-back is more efficient in environments with "bursty" write activity.
LSI recommends using the Write-back policy to achieve optimum performance int RAID 0, RAID 1, and RAID 10 configurations with transactional (random real-world) reads.

Please Register.

If you wish to add comments.