Write Policies for Host-side Flash Caches

18 Jun 2015

Write Policies for Host-side Flash Caches on FAST 2013.

This is another write operation related paper. While the Non-blocking Writes address the read-before-write problem by improving the parallelism in SSDs, this paper use Host-side Flash Caches by supporting synchronous write operations. A SSDs write cache is added to the network storage system, o that the write-back policy can be enabled:

write_back_ssd

Similar to the Non-blocking Writes paper, the author focus mainly on the data consistency issue when a write cache is introduced. The 3-dimentional trade-off for write caching policy is: Performance, Consistency, and Staleness.

trade-off_write-caching

There are two write-back policies.

The Ordered Write-back

In this write-back policy, the original order of the write are preserved in the write-back operation. This policy preserved better consistency with a greater cost. Because all the write on the same page need to be cached and destaged to networked storage.

Journaled Write-back

This policy combines multiple update into a single journal update, thus merge the write operations.