Drive letter problem

[P. Burrows]

Hi,

I wonder if someone can help me with this:

I have a problem with the driveletter mapping:

I bought a maxtor usb drive and gave it two partitions, and thus two
letters, lets call them A and B.

Then later I bought anohter usb drive, but it has only one partition,
lets call its letter C.

Now. If I switch the machine on and off or reboot, the letters get moved
around.

C now becomes A
A now becomes B
B now becomes C

Seems the only solution is to switch the drives on or off before booting
or starting.

Sure I could go to Disk Management and change the letter, but that only
lasts for the duration and becomes annoying to do all the time.

Isn't there a permanent way to tell XP to remember the damn names?

 

[bxf]

On my XP (SP2) system, Windows retains the drive letters that I
assigned under Disk Management. This is consistently true for both of
my USB HDDs as well as a USB DVD drive. I have noticed some
inconsistencies with respect to flash memory.

I did not do anything special to make this work, but I do wonder what
mechanism Windows uses to identify a particular drive so that it knows
which letter should be assigned to the device that has just been
connected. Is it some internal identifier, or perhaps a volume label?
If you have not already done so, why not try giving your devices two
different labels, just in case Windows uses these things to
differentiate between the drives.

 

[Vanguard \(NPI\)]

Hi,

I wonder if someone can help me with this:

I have a problem with the driveletter mapping:

I bought a maxtor usb drive and gave it two partitions, and thus two
letters, lets call them A and B.

Then later I bought anohter usb drive, but it has only one partition,
lets call its letter C.

Now. If I switch the machine on and off or reboot, the letters get moved
around.

C now becomes A
A now becomes B
B now becomes C

Seems the only solution is to switch the drives on or off before booting
or starting.

Sure I could go to Disk Management and change the letter, but that only
lasts for the duration and becomes annoying to do all the time.

Isn't there a permanent way to tell XP to remember the damn names?

You cannot/should not user A: or B: for fixed drives. Those are reserved
for use by removable media drives (i.e., floppy drives). Hard drives start
with the "C:" drive designator.

Use the Disk Management applet (diskmgmt.msc) to make sure you have valid
drive designators assigned to each of your fixed drives. A signature is
used in the MBR (master boot record) on each fixed disk to identify it.
That is why you can physically move around fixed disks to different
controller ports without their drive designators changing. Otherwise, the
BIOS assigns drive designators in the order: active partition on first
physically detected fixed disk, active partition on second physically
detected fixed disk, and so on for each active primary partition on each
found fixed disk, then go back and assign a drive designator to each logical
drive in an extended partition on the first fixed disk, the logical drives
in an extended partition in the second fixed disk, and so on. With the
BIOS/DOS method of drive designator assignment, adding another fixed disk
that had a primary partition (active) could result in changing drive
designators. It is likely that your BIOS has no support for USB-connected
mass storage devices. Windows NT relies on the drive signature to watch
where is a fixed disk that was known before. However, that only watches
where is the fixed disk, and repartitioning could still result in changed
drive designators.

If you have duplicated disk signatures or they don't match what is recorded
in the registry when the fixed disk got enumerated (like it was formatted on
another system or under a different instance of the OS), you may need to
recreate the disk signature. In the Disk Management applet, use the
"Action -> Rescan Disks" menu. I believe this will check for missing or
duplicate signatures and write new ones.

 

[P. Burrows]

On my XP (SP2) system, Windows retains the drive letters that I
assigned under Disk Management. This is consistently true for both of
my USB HDDs as well as a USB DVD drive.

Lucky you. Even when you have ha dit removed?

I have noticed some inconsistencies with respect to flash memory.
Hm.

I did not do anything special to make this work, but I do wonder what
mechanism Windows uses to identify a particular drive so that it knows
which letter should be assigned to the device that has just been
connected. Is it some internal identifier, or perhaps a volume label?

No idea - haven't SP2, but surely it would be an upgrade there.

If you have not already done so, why not try giving your devices two
different labels, just in case Windows uses these things to
differentiate between the drives.

Yeah, they have different name

 

[P. Burrows]

You cannot/should not user A: or B: for fixed drives. Those are reserved
for use by removable media drives (i.e., floppy drives). Hard drives start
with the "C:" drive designator.

"lets call them A and B." means its an example.

Use the Disk Management applet (diskmgmt.msc) to make sure you have valid
drive designators assigned to each of your fixed drives.

The fixed partitions never change letters, only on the two usb drives.

It is likely that your BIOS has no support for USB-connected
mass storage devices.

No support can be "can read and write to the drive but forgets the
letter"

If you have duplicated disk signatures or they don't match what is recorded
in the registry when the fixed disk got enumerated (like it was formatted on
another system or under a different instance of the OS), you may need to
recreate the disk signature. In the Disk Management applet, use the
"Action -> Rescan Disks" menu. I believe this will check for missing or
duplicate signatures and write new ones.

Rescan Disks had no effect (ie, it didn't change the juggling around
behaviour of the drives)

 

[bxf]

Lucky you. Even when you have ha dit removed?

Yup, all the time.

No idea - haven't SP2, but surely it would be an upgrade there.

Perhaps that's the fix.

 

[Vanguard \(NPI\)]

"lets call them A and B." means its an example.



The fixed partitions never change letters, only on the two usb drives.


No support can be "can read and write to the drive but forgets the
letter"



Rescan Disks had no effect (ie, it didn't change the juggling around
behaviour of the drives)

Just a guess, but are you connecting the USB hard drives through a USB hub?
Or are you connecting them directly to USB ports in the computer case?
While it might be possible to enumerate different *single* devices connected
to the USB ports in the case (because they go to a specific port on one of
the USB controllers so that port can be uniquely identified), I doubt
enumeration works through a hub. You cannot guarantee which order the USB
devices are detected through a hub. It's not like old SCSI devices (that
don't rely on auto-negotiate) where you could dial in a specific ID number
on the device (and then had to make sure none of the others used it). I'm
not sure auto-negotiation of device ID on USB channels is guaranteed to
enumerate devices in the same order for device IDs.

Because they are USB-connected, they are not enumerated until detection.
That is after Windows loads, loads the USB device, and then checks what is
connected through it. I don't know that the USB driver will report the
volumed ID (not volume name) to the OS but might just simply represent it by
the device ID that got assigned to it when it got detected. So you might
need to switch which USB ports to which you connect so the drives gets
enumerated under the USB controller in the same order that you want them to
get enumerated, and not use a hub.

Of course, an update might fix the problem. After all,
http://support.microsoft.com/?id=830752 notes problems with USB-connected
CD-ROM drives that are supposedly fixed by the service pack. From another
post in this thread, it sounds like you haven't updated Windows XP to the
latest service pack. I've also seen USB problems based on which driver was
used. Some folks found problems with the vendor's driver and Microsoft's
USB driver worked okay (the ones included in Windows), but other have had to
get the latest motherboard driver package to get a newer USB driver. For
example, see http://support.microsoft.com/?id=307070.

Do you have any mapped (network) drives? If so, see
http://support.microsoft.com/?id=297694. When assigning drive designators
to mapped drives, start at the end of the alphabet, or so high up that you
will never collide with newly added drives with their possibly numerous
partitions.

Are you connecting a USB 2.x external drive to a USB 1.1 port? While
hooking a USB 1.0/1 drive to a USB 2.x port should work (because USB 2.0 is
backwards compatible), it might not work the other way around (i.e., you
cannot manufacture hardware that is forward compatible with other hardware
or specifications that don't yet exist and which may significantly differ
from your old hardware or specifications).

I haven't waded through the SP-2 specifications as to what it fixed or
added, but I've heard that USB 2.0 got added in SP-2 (so you might have
problems with a USB 2.0 drive even if connected to a USB 2.0 capable port
but don't have SP-2 installed).

 

[Vanguard \(NPI\)]

Well, I did find:

http://support.microsoft.com/default.aspx?scid=kb;en-us;822603
http://support.microsoft.com/default.aspx?scid=kb;en-us;329632

which indicate that SP-1 had updates for USB support. If you have the
original Windows XP sans any service pack, looks like you'll need at least
SP-1.

For SP-2 at:

http://support.microsoft.com/default.aspx?scid=kb;en-us;811113

are listed lots of USB fixes.

However, if you have a non-Intel chipset on your motherboard, be sure to
download and install the latest chipset driver suite from your motherboard
maker's web site. Sometimes you even have to get a separate USB driver
download from them; for example, the chipset driver suite is sufficient if
you use the Windows-supplied USB drivers provided USB is supported in that
version of Windows, but you would need to get their USB drivers if you were
using, say, Window 98.

 

[bxf]

Vanguards' points reminded me of something I'd encountered in the past.

I'd noticed that if I plug a device (and this is where my earlier
reference to inconsistencies with flash memory may come in) into a
different port, the drive letter assignment may change. Since I keep my
drives plugged into the same respective ports most of the time (I just
power them off when not needed), I no longer have a drive letter
problem. In fact, when I disconnect my devices from my laptop, I make a
note of which device is plugged where so that I am able to reconnect
the same way.

I've also mentioned in another post that I suspect that even the order
in which devices are plugged may have some bearing on letter
assignment, but I've never pursued this matter enough to make a
definitive statement.