On Mon, Feb 6, 2012 at 3:47 PM, Robert McDermott
<rmcdermo@fhcrc.org> wrote:
Hello,
We a V3170 cluster with a 512GB Flash Cache module installed in each
controller. Each module is currently configured to cache normal data
(default setting):
flexscale.enable on
flexscale.lopri_blocks off
flexscale.normal_data_blocks on
We have a vfiler running on one controller that does very little normal
IO but has a very heavy metadata load due to poor application design.
This vfiler has poor performance and its function is critical. We are
thinking about switching to metadata only caching mode
(flexscale.lopri_blocks off, flexscale.normal_data_blocks off) to
improve its performance but have a couple of questions:
The Flash Cache best practices guide has the following verbage about
enabling metadata only mode:
"Because of the much larger size of Flash Cache, this mode is more
applicable to PAM I, the original 16GB DRAM–based Performance
Acceleration Module, than Flash Cache."
Does that mean that this setting doesn't apply (not
recommended/supported) for Flash Cache? but is for PAM I? Is using
metadata only mode a bad idea with a large flash cache module? If so why?
The best practices guide also indicates that it's recommended to have a
symmetrical number and size of modules between controllers in a cluster,
but it doesn't say anything about symmetrical cache mode settings. Is it
OK to have one controller's flash cache set to the normal data setting,
but the others flash cache set to metadata only? During a failover the
cache of the failed controller is essentially lost (doesn't follow it to
the remaining controller) so it doesn't seem like it would matter as
long as the cluster didn't stay in this failover state for a long period
of time. What are your thoughts on this?
Thanks in advance,
-Robert
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