RVilca wrote:
Hi,
I noticed that at moment of high load the time of reading is much more that time of writing, so I am considering to enable the Adaptive Flash Cache Option. We use SSD, FC and NL disk, but we have contention major in FC and the combination of FC enabled with tier 0. I have not experience with Adaptive Flash Cache and the implications in the current configuration. We have 2 arrays 3PAR 7400 FC and the hosts are connected by FC using SAN switches. We have two fabrics and the arrays are connected using ISL with a distance of several km using dark fiber. I haven't seen that the replica could be the problem (we use Remote Copy but not for LUNs with latency).
On the other hand the hosts are mostly blades inside chassises connected to SAN switches and in an vmware enviroment.
Regards.
The reason for higher read latency is that write will usually go straight to cache (as long as there is free pages to be used) while read usually has to go down to the storage media.
If you have available SSD capacity, using it for AO is in my experience the best use in 99 out of 100 cases.
If your FC is overloaded, then that will usually impact everything. Drives are to busy to destage write cache so there is no free cache pages for new writes.
If would look at AO and the output from srrgiodensity to understand which volumes are the heavy hitters and how much of that data is active.