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Number Of Requests Key

Occasional Advisor

Number Of Requests Key

Does anyone know what the NumberOfRequests key should be set to for p800 SAS RAID controller? We have it installed on a ML350 G5, with six 15K 300GB SAS disks in a raid 1+0 config.

These microsoft links, among others:

... say that the key controls the queue depth or number of concurrent requests to the controller, and that by default it's configured for low-end controllers. A p800 should be able to handle more, but how much more?

The relevant key is
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\\Parameters\Device\NumberOfRequests (REG_DWORD)

A few posts of configuration files include the setting, but not for our hardware and there's no discussion of it.

Thanks in advance.

Re: Number Of Requests Key

Did you ever get an answer to your question? Have you played around the setting yourself at all? I'm in the same boat.
Occasional Advisor

Re: Number Of Requests Key

We never found an answer and left it as is. It may have been a bit of a red herring, because the reg key wasn't on our server (maybe you need to create it?) and few people had heard of it. Here's a dump of our notes on it, if it's any help:



"Both SCSIport and Storport miniport drivers can use a
registry parameter to designate how much concurrency is
allowed on a device by device basis. The default is 16,
which is much too small for a storage subsystem of any
decent size unless quite a number of physical disks are
being presented to the operating system by the controller.
The maximum value is 255, but this is probably excessive
in most configurations. Increasing the value beyond the
needed amount results in wasted memory (that is, increased
memory footprint)."


This parameter allows you to specify the number of SRBs created
for a given adapter. This improves performance and allows Windows
to give more disk requests to a logical disk, which is most useful
for HW RAID adapters that have concurrency capabilities, because
each logical disk consists of multiple physical disks. However,
the default setting is often less than optimal for many high-speed
HW RAID disk arrays. Overall disk array performance can be
improved by setting NumberOfRequests to a value in the range of 32
to 96 (decimal). Set the following registry entry:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MINIPORT_ADAPTER\Parameters\DeviceN\NumberOfRequests (REG_DWORD)

Replace miniport_adapter with the specific adapter name. Make an
entry for each device, and in each entry replace DeviceN with
Device1, Device2, and so forth, depending on the number of devices
you are adding. A reboot is required for this setting to take
effect. For example, for two Emulex LP9000 miniport adapters whose
miniport driver name is lp6nds35, you would create the following
registry entries set to 96:



Designing RAID Adapters to Work with Windows

In addition, if a RAID miniport supports more than one outstanding
request per logical unit (LU) or virtual disk, the miniport must
control the queue depth.
* For SCSIport miniports, the NumberOfRequests registry setting
controls the queue depth for the entire adapter.
* With Storport, the queue is per LU and the miniport must set
the depth to an appropriate value by using
StorPortSetDeviceQueueDepth. Storport miniports also can
freeze and thaw the individual device queues or do so at the
adapter level. (Storport does not use the NumberOfRequests

proper settings for p800 raid controller

reg key above doesn't exist on our server
searched registry for 'numberofrequests', nothing

can't find documentation anywhere re: concurrency or
- userguide
- tech brief
- quickspecs
- google

Jay at hp support:
- windows tech support
- talked to 5 storage support guys, nobody heard of
- if it worked as well as Microsoft says, we'd very likely
already be using it
- can try a few different settings and see what results are
. proceed at own risk

google turns up a few reports of it being set to 80 by
admins of hp servers, but not for our specific controller