Disk admin and required on disk structs?

NTFSD
1

I’m in the process of trying to write a windows file system from
scratch. Everything that I’ve been reading suggests that the on disk
structure, even of the boot block, is up to me, as windows I\O manager
will merely request that each filesystem driver let it know if the FSD
can mount the filesystem. I came across the Disk Administrator today
which allows you to change drive letters. The article claimed that DA
wrote a file system signature to that partition’s boot sector to allow
it to identify that disk and relate it to the assigned drive letter.
This would imply that DA knows something about the format of the boot
sector. Yet, when comparing FAT, FAT32, and NTFS, the boot sector’s
don’t look very similar. The only thing I can see that would imply a
signature is the 15h location, the Media Descriptor. Or perhaps this is
stored in the partition table, in which case, I don’t need to worry
about DA overwriting the data on my file system. Are there any required
on disk fields that windows needs from me, or locations that it expects
to have certain data?
Thanks,
Allan

2

I think that this is about the MFT’s “partition type” values. You can use 7
(IFS) for any your filesystem, NTFS also uses it. FAT requires other values.

Maxim Shatskih, Windows DDK MVP
StorageCraft Corporation
xxxxx@storagecraft.com
http://www.storagecraft.com

----- Original Message -----
From: “Allan Graves”
To: “Windows File Systems Devs Interest List”
Sent: Friday, July 29, 2005 11:42 PM
Subject: [ntfsd] Disk admin and required on disk structs?

> I’m in the process of trying to write a windows file system from
> scratch. Everything that I’ve been reading suggests that the on disk
> structure, even of the boot block, is up to me, as windows I\O manager
> will merely request that each filesystem driver let it know if the FSD
> can mount the filesystem. I came across the Disk Administrator today
> which allows you to change drive letters. The article claimed that DA
> wrote a file system signature to that partition’s boot sector to allow
> it to identify that disk and relate it to the assigned drive letter.
> This would imply that DA knows something about the format of the boot
> sector. Yet, when comparing FAT, FAT32, and NTFS, the boot sector’s
> don’t look very similar. The only thing I can see that would imply a
> signature is the 15h location, the Media Descriptor. Or perhaps this is
> stored in the partition table, in which case, I don’t need to worry
> about DA overwriting the data on my file system. Are there any required
> on disk fields that windows needs from me, or locations that it expects
> to have certain data?
> Thanks,
> Allan
>
> —
> Questions? First check the IFS FAQ at
https://www.osronline.com/article.cfm?id=17
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