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Home > Archive > Data Storage > November 2004 > High Level vs Low Level Formatting (was Format Iomega Rev as NTFS?)
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High Level vs Low Level Formatting (was Format Iomega Rev as NTFS?)
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| Jon Forrest 2004-11-04, 5:45 pm |
| Emmet Gray wrote:
> Has anybody tried to do a low-level reformat (and fdisk, I'd assume)
> of an Iomega Rev drive to NTFS?
A file system reformat is a high-level reformat. IDE hard drives
are not low-level formatable without special equipment.
The way to think about this is as follows:
Picture a newly paved parking lot. Only parking
attendants can park cars there, and they can only
do it by putting a car in a specific parking space.
Low level formatting is equivalent to painting
the parking space lines on a newly paved parking lot.
High level formatting is equivalent to forming
collections of parking spaces, such as in a big
lot shared by a number of stores, where some of the
spaces are only to be used by store X, and others are
only to be used by store Y.
Since creating a file system is just a matter of
organizing existing disk blocks, there's no
repainting of the blocks necessary.
These days the only low level formatting that's commonly
done is on floppy and SCSI disks. My guess is that
the reason why it's not possible on IDE disks is because
the electronic logic for doing so is not built into
the standard IDE "controllers" in the disk drives, in
order to keep the controllers simple. Disk manufacturers
have special equipment that can do this.
Jon Forrest
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| Robert Wessel 2004-11-06, 2:45 am |
| Jon Forrest <forrest@ce.berkeley.edu> wrote in message news:<418A685D.3020907@ce.berkeley.edu>...
> A file system reformat is a high-level reformat. IDE hard drives
> are not low-level formatable without special equipment.
> (...)
> These days the only low level formatting that's commonly
> done is on floppy and SCSI disks. My guess is that
> the reason why it's not possible on IDE disks is because
> the electronic logic for doing so is not built into
> the standard IDE "controllers" in the disk drives, in
> order to keep the controllers simple. Disk manufacturers
> have special equipment that can do this.
Not exactly true. All current IDE hard drives have all the hardware
and firmware on board to do the low level format. The manufacturer
just doesn't tell people how to get at it. As a practical matter you
cannot do a low level format of a modern hard drive with anything
other than the exact set of heads that it will live its life with.
So the "special equipment" is mostly just software that knows which
special commands to actually send to the drive. I wouldn't be
surprised if in some cases it may be necessary to enable this via a
diagnostic port in some way, but I know that's not the case for
several major lines of IDE drives.
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| Robert Wessel 2004-11-09, 8:45 pm |
| Jon Forrest <forrest@ce.berkeley.edu> wrote in message news:<418FF9DB.4090109@ce.berkeley.edu>...
> I'm surprised word hasn't gotten out on how to do it.
> Not even SpinRite tries to do it (see below).
It's not that hard to get out of the manufacturers, at least if you're
building boxes, but the details tend to be different on every minor
revision of the drive.
> Sure, but since heads are never changed I don't see this being
> a major obstacle. Also, why can SCSI controllers do it?
Don't think that Format_Unit actually does a low level format on most
SCSI drives. SCSI drives have a "middle level" format where logical
blocks are assigned to physical blocks, interleave set, bad blocks are
remapped, etc. Format_Unit will update that stuff on all drives, but
not the "real" low level format on modern drives.
Again, there's typically a secret way to really do a low-level.
> The real question is why somebody would want to do a low level format
> in the first place. The only reason I can think of would be if the
> disk has developed a bunch of bad blocks, but chances are that's a sign
> of future failure, and low level formatting would only postpone the
> inevitable. A low level format doesn't erase all the data on the disk,
> but it makes the data very hard to find. However, people with big
> security problems would not accept a low level format as a way
> to erase a disk.
There are darn few reasons for an end-user to do a low-level (which is
why the capability has gone away), but if you refurbish a drive, or
have one that's been subject to extreme environmental conditions
(heat, cold, shock, vibration) for an extended period of time, it may
be useful.
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