7.8 MB freespace

[Lil' Dave]

I don't know how the 7.8mb unallocated space got there, (at the front end

of my 2nd, slave, hd),
but, any ideas on how best to get rid of it, ...or just leave it there ?
http://www.rk73.wanadoo.co.uk/
I don't like the idea of having a dynamically allocated drive letter that
comes after the others, and then merging it with another drive, leaving
that space not really at the end of the drive, if u c wot i mean

regards, Richard

Richard:
In response to a query similar to yours, the following posting was made to
one of the XP newsgroups (not sure if it was this particular one) a few
months ago...

"That 8 MB partition is auto-created to handle dynamic disk information.
When a disk is converted to dynamic in the Disk Management snapin,
information regarding the configuration and any dependencies (e.g. software
RAID) are stored on disk at the end of the drive. This is how a drive can
be moved from one dynamic disk array to another and be recognized as
foreign drive.

Best regards,

Mike Truitt
Microsoft Corporation"
------------------------

Is the above true?
I found similar 7.8 MB freespace on numerous hard drives with single
extended partitions. None of which saw XP or NT. Extended partitions and
their logical drives were created with PM. Or is PM creating this for XP/NT
in case its needed?

 

[Mike Ching]

Richard:
In response to a query similar to yours, the following posting was made to
one of the XP newsgroups (not sure if it was this particular one) a few
months ago...

"That 8 MB partition is auto-created to handle dynamic disk information.
When a disk is converted to dynamic in the Disk Management snapin,
information regarding the configuration and any dependencies (e.g. software
RAID) are stored on disk at the end of the drive. This is how a drive can
be moved from one dynamic disk array to another and be recognized as
foreign drive.

Best regards,

Mike Truitt
Microsoft Corporation"
------------------------

Is the above true?
I found similar 7.8 MB freespace on numerous hard drives with single
extended partitions. None of which saw XP or NT. Extended partitions and
their logical drives were created with PM. Or is PM creating this for XP/NT
in case its needed?

My guess is that the response is to a different question. The 7.8MB space is
the size of the smallest partition that can be created in a modern drive and
seems to be reserved for the creation of a primary partition when a disk
only has an extended partition. It was smaller in the days when disks were
measured in MB instead of today's GB. In response to the OP, you can't get
rid of it.

 

[Eric Gisin]

In response to a query similar to yours, the following posting was made to
one of the XP newsgroups (not sure if it was this particular one) a few
months ago...

"That 8 MB partition is auto-created to handle dynamic disk information.
When a disk is converted to dynamic in the Disk Management snapin,
information regarding the configuration and any dependencies (e.g. software
RAID) are stored on disk at the end of the drive. This is how a drive can
be moved from one dynamic disk array to another and be recognized as
foreign drive.

Mike Truitt
Microsoft Corporation"

Is the above true?
I found similar 7.8 MB freespace on numerous hard drives with single
extended partitions. None of which saw XP or NT. Extended partitions and
their logical drives were created with PM. Or is PM creating this for XP/NT
in case its needed?

Not quite true. It will reserve 1-8GB on SCSI drives. My SCSI has 6GB at the
end.

IDE drives are designed so that logical and physical CHS both multiply out to
the total LBA. Ie, they are always multiples of 255*63*512B = 7.8GB. SCSI
does not since they are not inherently CHS.

Dynamic disks require 1GB for the LDM database, Basic disk do not.

I have edited the partition table to extend the last partition, and it works
fine under NT/2K/XP.

 

[Folkert Rienstra]

My guess is that the response is to a different question. The 7.8MB space is
the size of the smallest partition that can be created in a modern drive and
seems to be reserved for the creation of a primary partition when a disk
only has an extended partition.

It was smaller in the days when disks were measured in MB instead of
today's GB.

Because of geometry translation.
Up to 540MB, heads used to be 16 max. After that, heads became 256 max.

On smaller drives (smaller than 8GB, and for number of heads to be smaller,
probably significantly smaller than 8GB, like less than 4 GB) heads can still
be smaller than 256 though, dependent on translation type used in BIOS.

Because a cylinder size (partitions are usually defined by cylinder bound-
aries and by full cylinders) depends on the number of heads setup in BIOS.
Depending on CHS translation chosen, the number of P-cylinders on the
drive are bit-shifted down lower to the first number lower than or equal
to 1024, which can result in less than the maximum allowed number of
heads, thus minimizing the size of one cylinder worth.
LBA(-assist) will just re-calculate the logical CHS by dividing the logical
number of sectors on the drive by first sectors and then heads, using
the maximum number allowed for CHS sectors and then for CHS heads.

EG 8192*16*63 (4GB) can be bit-shifted to 1024*128*63 using Large
vs the 512*255*63 by using LBA(-assist).

Using Large will only waste 128*63*512B = 3.9MB

 

[Folkert Rienstra]

Not quite true. It will reserve 1-8GB on SCSI drives.

My SCSI has 6GB at the end.

MB, not GB. And your 6MB is probably 'orphan' space and not what he is talking about.

What he's talking about is probably a (logical) cylinder worth at the start of the drive
so it depends on the size of the cylinder. For drives over 8GB this will then be limited
to 7.8MB. For drives smaller than 8GB it depends on the number of heads in BIOS.

IDE drives are designed so that logical and physical CHS both multiply out to
the total LBA.

Utter nonsense.
For the very first (40GB) harddrive that I picked this wasn't already the case:
80,418,240 sectors, not a full complement of 255*63 size cylinders.
And since logical and physical CHS are both limited to 8GB, that's just another
reason why that's bloody nonsense.

Ie, they are always multiples of 255*63*512B = 7.8GB.

That's MB, not GB. And for smaller drives with less than 255
logical heads defined in BIOS it is obviously less than 7.8MB.

SCSI does not since they are not inherently CHS.

Nonsense.
Neither are IDE anymore. It's a logical cylinder worth in both cases.
Or less than a logical cylinder worth if speaking of 'orphan space' at
the end. Nothing to do with IDE vs SCSI.

Dynamic disks require 1GB for the LDM database, Basic disk do not.

Again, presumably that's MB, not GB.

I have edited the partition table to extend the last partition, and it works
fine under NT/2K/XP.

So either you have a drive smaller than 8GB or you edited the LBA values.