Immediate reporting error

[Rodney Myers]

I have an HP Smart Array controller with 512 MB cache upgrade installed in an Integrity rx4640 Itanium machine.

I am attempting to enable "immediate reporting" on that controller to measure the impact on performance. I use the command "sudo scsictl -a -m ir=1 -m ir /dev/rdsk/c5t0d0"

However, I see the error message:
"scsictl: Device ioctl (: Device ioctl () error: Invalid argument"

I don't know if it is relevant, but the disk is in use at the moment. I can't easily unmount the active filesystems.

Will someone give me a tip about how to resolve this error?

Thanks,
Rodney

[Hein van den Heuvel]

Seems reasonable to me.

The scsictl command is intended to control 'real disks'.

The Smart Array has its own management tools and 'smarts'. Therefor 'immmediate reporting' (switching on write behind caching) is an 'Invalid Argument'.

Please use the Smart Array tools to manage it.

hth,
Hein.

[Rodney Myers]

Unfortunately I didn't see an option to enable immediate reporting using the smart array utilities. Is immediate reporting enabled by default for the smart array? FYI, the kernal tunable for immediate reporting is set to zero on my system.

[Hein van den Heuvel]

It could be a terminology confusion.

The "immediate reporting" corresponds to enabling write caching which in turn corresponds to a non-100% read cache.

See:
http://docs.hp.com/en/J6369-90036/J6369-90036.pdf

http://docs.hp.com/en/J6369-90036/index.html
detail:
http://docs.hp.com/en/J6369-90036/ch04s02.html#chdggiab

Example:
saconfig /dev/ciss7 -C 50



Also:
http://h18004.www1.hp.com/products/servers/proliantstorage/arraycontrollers/smartarray6400/index.html

hth,
Hein.

[Rodney Myers]

Thanks for responding again. I did look at those documents. It probably is a terminology issue.

Currently the smart array cache is enabled, with 25% dedicated for read cache, 75% dedicated for write cache. I have changed no other setting.

In case I have misunderstood you or the documentation, please verify that this configuration will give write behind caching aka "immediate reporting" for the smart array. Thank you.

[Hein van den Heuvel · Accepted solution]

That's how I understand it.

With memory available for write cache the smart array will immediatly report a write IO as completed as soon as the data is in its cache.
A battery protects it there for up to 4 days.

75% of cache dedicated to write cache sounds like a lot but may be justified when write happen in large bursts (sync).

If you have more then 128MB cache memory, then you might reduce to 50/50.

Ideally you would run a week (or day) one way, and an other period without and compare results (transaction response times, throughput, idle time).

hth,
Hein van den Heuvel
HvdH Performance Consulting

http://h18004.www1.hp.com/products/quickspecs/11587_div/11587_div.html#Technical%20Specifications

[Rodney Myers]

Thanks for the information.