Get Cluster size

NTDEV
1

Hi,

I am working on an upper filter driver taking diskperf as base.
I want to know how can I calculate cluster size(allocation unit size).
I know that using “GetDiskFreeSpace” I can get the desired output, but its useful in user mode. I want it to work at the kernel level.
Is there any IOCTL or any function that will help me to find the cluster size?

2

The cluster size is a file system/volume attribute so unless you have a
mapping of your disk into a volume so you can call
ZwQueryVolumeInformationFile or the underlying IRP’s you are out of
luck.

Don Burn
Windows Filesystem and Driver Consulting
Website: http://www.windrvr.com
Blog: http://msmvps.com/blogs/WinDrvr

“xxxxx@gmail.com” wrote in message
news:xxxxx@ntdev:

> Hi,
>
> I am working on an upper filter driver taking diskperf as base.
> I want to know how can I calculate cluster size(allocation unit size).
> I know that using “GetDiskFreeSpace” I can get the desired output, but its useful in user mode. I want it to work at the kernel level.
> Is there any IOCTL or any function that will help me to find the cluster size?

3

Hi,

Yes I am working on upper volume filter driver so can I use “ZwQueryVolumeInformationFile”?

4

No in that case use IRP_MJ_QUERY_VOLUME_INFORMATION. I can’t swear this
will work, but I would start there.

Don Burn
Windows Filesystem and Driver Consulting
Website: http://www.windrvr.com
Blog: http://msmvps.com/blogs/WinDrvr

“xxxxx@gmail.com” wrote in message
news:xxxxx@ntdev:

> Hi,
>
> Yes I am working on upper volume filter driver so can I use “ZwQueryVolumeInformationFile”?

5

Hi,

I am unable to get any help regarding “IRP_MJ_QUERY_VOLUME_INFORMATION” for upper volume filter, can you provide me any example or any sample that make use of it.

6

Hi,

Does any one knows how to get the cluster size in upper volume filter driver?

Thanks in advance.

7

xxxxx@gmail.com wrote:

Does any one knows how to get the cluster size in upper volume filter driver?

Did you not like the answer you got earlier in the week? The whole
concept of a “cluster” is a file system concept. It is handled in
drivers ABOVE you. The concept of a “cluster” simply does not exist at
the volume level.

–
Tim Roberts, xxxxx@probo.com
Providenza & Boekelheide, Inc.