VA7100 optimizations

[mgais]

Hello,

I'm trying to optimize the performance of a VA7100, plugged to a RP5450 that runs HP-UX 11.11.
The machine is used as Rational Clearcase VOB server (a software control management application).
I'd be interested in two types of optimizations:

1) VA settings like:
Queue Full Threshold
Enable Prefetch
Write/Read Cache Enable

2) Kernel settings (to match VA capabilities):
max_fcp_reqs
scsi_max_qdepth
default_disk_ir

And finally, should I mount the filesystem with mincache=direct,convosync=direct options as the HP-UX performance cookbook suggests?

TIA

[Srinivasa_6]

Hello,

I can tell you about the array side optimizations that you've asked about.

2) The QFT is usually set using the following formula (At least HP support recommends this type of setting)

2*(# of disks in an RG) / (controller host ports)

Since VA7100 has just a single RG, a single enclosure and 2 host ports, the formula essentially becomes:

2*(# of disks in the array enclosure) / 2

So, a QFT value of 15 to 20 is ideal.

2) Prefetch should be enabled. This is the array caching algorithm to detect sequential reads and prefetch data ahead of time. I guess, prefetch is enabled by default. So, leave it as it is.

3) Write/Read cache settings also better not be changed. The default settings are, write and read cache enabled. While there's no provision to disable read cache, write cache can be turned off. But this is not advisable since the array will go into a write through mode. In this mode, all host writes directly go to the disk and the latency increases/throughput decreases.

Hope that helps.

[mgais]

Hello,

thank you for your suggestions.
I think my VA has default settings and:
-Queue Full Threshold Maximum is set to 4096
-Write Cache Enable is set to False and
-Enable Prefetch is set to False.

So I guess it's quite on the "conservative" side...

Regards

[mgais]

I've to slightly amend my previous message, since there I reported only the QFT Maximum. The QFT is actually set at 750.
Hovever the substance is that it seems still too big by a factor ~20.

[Arend Lensen]

Massimo,

Don't set the QFT to low as that would throttle down the iops. When there's only a single server attached and you don't have hundreds of luns you can try to keep using the default 750. Checkout the command view manual and create the FRONT-END performance logs, use the helpfile for the armperf command for the right syntax. When you have set the QFT too low you will see queue-full reponses sent to the host. When QWT is set to high you could see frontend-aborts.

kind regards,
Arend

[mgais]

Arend,

first, thank you for your hint.

What parameters do you exactly suggest to
monitor in the FRONTEND category?
Command Aborts Received, Commands Timed Out, Queue Full Status ?

Also, what do you think about kernel settings? Do they have to be tuned according to the disk array, or may I rely on defaults being at least decent setting?