Randy Bias wrote:
On Sep 29, 2006, at 6:24 AM, Roch wrote:
Keith Clay writes:
On Sep 29, 2006, at 2:41 AM, Roch wrote:
IMO, RAIDZn should perform admirably on the write loads.
The random reads aspects is more limited. The simple rule of
thumb is to consider that a RAIDZ group will deliver random
read IOPS with the performance characteristic of single
device. That rule does not apply to either read or write
streaming data but only for small random reads pattern.
If that means you need to construct small RAIDZ groups
then do consider mirroring as an alternative.
So, mirroring, on jbods would give me the same/better performance
than raidzn? Would that apply to fc drives or also to SATA?
On small random read loads ? It's much better to use mirroring
and that's Independant on device type.
What about the case of an iSCSI LUN? Does this change? I get that
while local to the system a read from a mirror versus a RAIDZ pool is
desirable, but would an IP network introduce enough latency that the
difference is negligible? And wouldn't I get better aggregate
performance across more spindles for multiple iSCSI LUNs than trying
to create a mirror pair for each individual iSCSI LUN?
I hate to say but ... it depends. How fast is the iSCSI connection.
There are too many variables in the stack - network, array, backend
target, iSCSI stack, etc. - to make a generalization.
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