[gentoo-user] Strange partition on USB stick

[gentoo-user] Strange partition on USB stick

[Mick]

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I can't recall if I asked this before, but I am looking at a partition on a 
USB stick which seems to have a FAT16 fs on it and in parted says:

==================================================
Model: Crucial Gizmo! overdrive (scsi)
Disk /dev/sdb: 1023MB
Sector size (logical/physical): 512B/512B
Partition Table: loop

Number  Start  End     Size    File system  Flags
 1      0.00B  1023MB  1023MB  fat16
==================================================

What does "Partition Table: loop" mean?


fdisk -l is more confusing:
==================================================
Disk /dev/sdb: 1022 MB, 1022623744 bytes
32 heads, 61 sectors/track, 1023 cylinders, total 1997312 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x69737369

This doesn't look like a partition table
Probably you selected the wrong device.

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1   ?  1869771365  2038460886    84344761   69  Unknown
/dev/sdb2   ?  1701519481  3571400945   934940732+  73  Unknown
/dev/sdb3   ?        2573        2573           0   74  Unknown
/dev/sdb4               0  3435113471  1717556736    0  Empty

Partition table entries are not in disk order
==================================================

What are the partitions shown as sdb1-4?

Also Id 73 and 74 are I think reserved Ids?  Id 69 is I think Novell Netware 
5+ (according to: 
http://www.win.tue.nl/~aeb/partitions/partition_types-1.html) not FAT16.

I am not sure I understand what it is showing me.  

BTW, cfdisk spews it out right from the start:
==================================================
FATAL ERROR: Bad primary partition 1: Partition begins after end-of-disk
                          Press any key to exit cfdisk
==================================================

So, does it have a partition table?  How can you explain the fdisk output?
-- 
Regards,
Mick

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Re: [gentoo-user] Strange partition on USB stick

[Adam Carter]

If the data is important, I'd use ddrescue to create an image of the
drive, then run testdisk over that image to see if it can untangle the
partition table mess. Both are in portage.

Re: [gentoo-user] Strange partition on USB stick

[Mick]

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On Tuesday 04 Oct 2011 04:39:45 Adam Carter wrote:
> If the data is important, I'd use ddrescue to create an image of the
> drive, then run testdisk over that image to see if it can untangle the
> partition table mess. Both are in portage.

Well, that's the thing:  I'm not sure that there is a mess.  At least not as 
far as parted is concerned, which can read the partition table properly.  

I suspect that fdisk (unlike parted) is not capable of reading the device 
correctly.

I forgot to say that when mounted the USB stick shows not partitions (i.e. 
there is no sdb1, sdb2, etc.)  To access the fs I must do something like:

pmount /dev/sdb

and then all is lists under /media/sdb.  It is like a big floppy.
-- 
Regards,
Mick

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Re: [gentoo-user] Strange partition on USB stick

[Paul Hartman]

On Tue, Oct 4, 2011 at 12:18 AM, Mick <michaelkintzios@gmail.com> wrote:
> On Tuesday 04 Oct 2011 04:39:45 Adam Carter wrote:
>> If the data is important, I'd use ddrescue to create an image of the
>> drive, then run testdisk over that image to see if it can untangle the
>> partition table mess. Both are in portage.
>
> Well, that's the thing:  I'm not sure that there is a mess.  At least not as
> far as parted is concerned, which can read the partition table properly.
>
> I suspect that fdisk (unlike parted) is not capable of reading the device
> correctly.
>
> I forgot to say that when mounted the USB stick shows not partitions (i.e.
> there is no sdb1, sdb2, etc.)  To access the fs I must do something like:
>
> pmount /dev/sdb
>
> and then all is lists under /media/sdb.  It is like a big floppy.

I think that's your answer. The "partition table" looks funny because
it isn't one. :) It is somewhat common. I've had some myself that are
like that.

Re: [gentoo-user] Strange partition on USB stick

[Alan McKinnon]

On Tue, 4 Oct 2011 00:27:50 -0500
Paul Hartman <paul.hartman+gentoo@gmail.com> wrote:

> On Tue, Oct 4, 2011 at 12:18 AM, Mick <michaelkintzios@gmail.com>
> wrote:
> > On Tuesday 04 Oct 2011 04:39:45 Adam Carter wrote:
> >> If the data is important, I'd use ddrescue to create an image of
> >> the drive, then run testdisk over that image to see if it can
> >> untangle the partition table mess. Both are in portage.
> >
> > Well, that's the thing:  I'm not sure that there is a mess.  At
> > least not as far as parted is concerned, which can read the
> > partition table properly.
> >
> > I suspect that fdisk (unlike parted) is not capable of reading the
> > device correctly.
> >
> > I forgot to say that when mounted the USB stick shows not
> > partitions (i.e. there is no sdb1, sdb2, etc.)  To access the fs I
> > must do something like:
> >
> > pmount /dev/sdb
> >
> > and then all is lists under /media/sdb.  It is like a big floppy.
> 
> I think that's your answer. The "partition table" looks funny because
> it isn't one. :) It is somewhat common. I've had some myself that are
> like that.
> 

I have a 4G Sandisk that does that too. It does everything a regular
USB stick does except a) create a proper partition table and b) be
booted from

-- 
Alan McKinnnon
alan.mckinnon@gmail.com

Re: [gentoo-user] Strange partition on USB stick

[Mick]

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On Tuesday 04 Oct 2011 07:53:47 Alan McKinnon wrote:
> On Tue, 4 Oct 2011 00:27:50 -0500
> 
> Paul Hartman <paul.hartman+gentoo@gmail.com> wrote:
> > On Tue, Oct 4, 2011 at 12:18 AM, Mick <michaelkintzios@gmail.com>
> > 
> > wrote:
> > > On Tuesday 04 Oct 2011 04:39:45 Adam Carter wrote:
> > >> If the data is important, I'd use ddrescue to create an image of
> > >> the drive, then run testdisk over that image to see if it can
> > >> untangle the partition table mess. Both are in portage.
> > > 
> > > Well, that's the thing:  I'm not sure that there is a mess.  At
> > > least not as far as parted is concerned, which can read the
> > > partition table properly.
> > > 
> > > I suspect that fdisk (unlike parted) is not capable of reading the
> > > device correctly.
> > > 
> > > I forgot to say that when mounted the USB stick shows not
> > > partitions (i.e. there is no sdb1, sdb2, etc.)  To access the fs I
> > > must do something like:
> > > 
> > > pmount /dev/sdb
> > > 
> > > and then all is lists under /media/sdb.  It is like a big floppy.
> > 
> > I think that's your answer. The "partition table" looks funny because
> > it isn't one. :) It is somewhat common. I've had some myself that are
> > like that.
> 
> I have a 4G Sandisk that does that too. It does everything a regular
> USB stick does except a) create a proper partition table and b) be
> booted from

I guess what I'm asking is:

If there isn't a partition table, then why fdisk sees /dev/sdb1-4 with 
somewhat strange ID types?  What is it that it interprets as 4 partitions?
-- 
Regards,
Mick

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Re: [gentoo-user] Strange partition on USB stick

[Mick]

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On Tuesday 04 Oct 2011 06:27:50 Paul Hartman wrote:
> On Tue, Oct 4, 2011 at 12:18 AM, Mick <michaelkintzios@gmail.com> wrote:
> > On Tuesday 04 Oct 2011 04:39:45 Adam Carter wrote:
> >> If the data is important, I'd use ddrescue to create an image of the
> >> drive, then run testdisk over that image to see if it can untangle the
> >> partition table mess. Both are in portage.
> > 
> > Well, that's the thing:  I'm not sure that there is a mess.  At least not
> > as far as parted is concerned, which can read the partition table
> > properly.
> > 
> > I suspect that fdisk (unlike parted) is not capable of reading the device
> > correctly.
> > 
> > I forgot to say that when mounted the USB stick shows not partitions
> > (i.e. there is no sdb1, sdb2, etc.)  To access the fs I must do
> > something like:
> > 
> > pmount /dev/sdb
> > 
> > and then all is lists under /media/sdb.  It is like a big floppy.
> 
> I think that's your answer. The "partition table" looks funny because
> it isn't one. :) It is somewhat common. I've had some myself that are
> like that.

If there isn't a partition table, then why fdisk sees /dev/sdb1-4 with 
somewhat strange ID types?
-- 
Regards,
Mick

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Re: [gentoo-user] Strange partition on USB stick

[Paul Hartman]

On Tue, Oct 4, 2011 at 1:58 AM, Mick <michaelkintzios@gmail.com> wrote:
> On Tuesday 04 Oct 2011 06:27:50 Paul Hartman wrote:
>> On Tue, Oct 4, 2011 at 12:18 AM, Mick <michaelkintzios@gmail.com> wrote:
>> > On Tuesday 04 Oct 2011 04:39:45 Adam Carter wrote:
>> >> If the data is important, I'd use ddrescue to create an image of the
>> >> drive, then run testdisk over that image to see if it can untangle the
>> >> partition table mess. Both are in portage.
>> >
>> > Well, that's the thing:  I'm not sure that there is a mess.  At least not
>> > as far as parted is concerned, which can read the partition table
>> > properly.
>> >
>> > I suspect that fdisk (unlike parted) is not capable of reading the device
>> > correctly.
>> >
>> > I forgot to say that when mounted the USB stick shows not partitions
>> > (i.e. there is no sdb1, sdb2, etc.)  To access the fs I must do
>> > something like:
>> >
>> > pmount /dev/sdb
>> >
>> > and then all is lists under /media/sdb.  It is like a big floppy.
>>
>> I think that's your answer. The "partition table" looks funny because
>> it isn't one. :) It is somewhat common. I've had some myself that are
>> like that.
>
> If there isn't a partition table, then why fdisk sees /dev/sdb1-4 with
> somewhat strange ID types?

It's misinterpreting the data that happens to be there because it
makes the assumption that it's a partition table even though it's not.

You can create a real partition table on that device and reformat, if
you want. (Note that some flash-based devices suffer degraded
performance if you repartition or reformat them because they come with
specially-aligned FAT tables from the factory)

Re: [gentoo-user] Strange partition on USB stick

[Mick]

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On Tuesday 04 Oct 2011 17:18:18 Paul Hartman wrote:
> On Tue, Oct 4, 2011 at 1:58 AM, Mick <michaelkintzios@gmail.com> wrote:
> > On Tuesday 04 Oct 2011 06:27:50 Paul Hartman wrote:
> >> On Tue, Oct 4, 2011 at 12:18 AM, Mick <michaelkintzios@gmail.com> wrote:
> >> > On Tuesday 04 Oct 2011 04:39:45 Adam Carter wrote:
> >> >> If the data is important, I'd use ddrescue to create an image of the
> >> >> drive, then run testdisk over that image to see if it can untangle
> >> >> the partition table mess. Both are in portage.
> >> > 
> >> > Well, that's the thing:  I'm not sure that there is a mess.  At least
> >> > not as far as parted is concerned, which can read the partition table
> >> > properly.
> >> > 
> >> > I suspect that fdisk (unlike parted) is not capable of reading the
> >> > device correctly.
> >> > 
> >> > I forgot to say that when mounted the USB stick shows not partitions
> >> > (i.e. there is no sdb1, sdb2, etc.)  To access the fs I must do
> >> > something like:
> >> > 
> >> > pmount /dev/sdb
> >> > 
> >> > and then all is lists under /media/sdb.  It is like a big floppy.
> >> 
> >> I think that's your answer. The "partition table" looks funny because
> >> it isn't one. :) It is somewhat common. I've had some myself that are
> >> like that.
> > 
> > If there isn't a partition table, then why fdisk sees /dev/sdb1-4 with
> > somewhat strange ID types?
> 
> It's misinterpreting the data that happens to be there because it
> makes the assumption that it's a partition table even though it's not.
> 
> You can create a real partition table on that device and reformat, if
> you want. (Note that some flash-based devices suffer degraded
> performance if you repartition or reformat them because they come with
> specially-aligned FAT tables from the factory)

Interesting!  I didn't know that.

I have repartitioned USB sticks in the past, but did not notice any change in 
performance - to be honest I didn't measure it.  I assume then that if I were 
to re-partition for any reason I would need to stick to exactly the same start 
& finish shown by parted.

Re-formatting it ought to be OK though, as long as the fat16 shown by parted 
is correct. 
-- 
Regards,
Mick

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Re: [gentoo-user] Strange partition on USB stick

[Paul Hartman]

On Tue, Oct 4, 2011 at 1:39 PM, Mick <michaelkintzios@gmail.com> wrote:
> On Tuesday 04 Oct 2011 17:18:18 Paul Hartman wrote:
>> You can create a real partition table on that device and reformat, if
>> you want. (Note that some flash-based devices suffer degraded
>> performance if you repartition or reformat them because they come with
>> specially-aligned FAT tables from the factory)
>
> Interesting!  I didn't know that.
>
> I have repartitioned USB sticks in the past, but did not notice any change in
> performance - to be honest I didn't measure it.  I assume then that if I were
> to re-partition for any reason I would need to stick to exactly the same start
> & finish shown by parted.
>
> Re-formatting it ought to be OK though, as long as the fat16 shown by parted
> is correct.

I think filesystems other than FAT are aligned well already, assuming
your partitions are aligned, but with FAT there are some hoops you
must jump through.

There is a tool called flashbench that can test your drive
(destructively!) and figure out the most optimal block sizes. Here's a
great article about it and optimizing USB flash drives in general:
https://lwn.net/Articles/428584/

And here is a forum thread about figuring out the FAT alignment:
http://www.patriotmemory.com/forums/showthread.php?3696

The SD council makes a tool for MS Windows that optimally formats and
securely erases SD cards. Might be interesting to compare the results
of its format to a standard fdisk and mkfs.vfat in linux.

One thing I'm going to do next time I get a new SD card or flash drive
is take a snapshot of the boot sector/partition tables/FAT tables so
if I ever want to reformat it to FAT, I can restore the -- presumably
optimal -- factory layout.

Re: [gentoo-user] Strange partition on USB stick

[Mick]

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On Tuesday 04 Oct 2011 20:36:06 Paul Hartman wrote:
> On Tue, Oct 4, 2011 at 1:39 PM, Mick <michaelkintzios@gmail.com> wrote:
> > On Tuesday 04 Oct 2011 17:18:18 Paul Hartman wrote:
> >> You can create a real partition table on that device and reformat, if
> >> you want. (Note that some flash-based devices suffer degraded
> >> performance if you repartition or reformat them because they come with
> >> specially-aligned FAT tables from the factory)
> > 
> > Interesting!  I didn't know that.
> > 
> > I have repartitioned USB sticks in the past, but did not notice any
> > change in performance - to be honest I didn't measure it.  I assume then
> > that if I were to re-partition for any reason I would need to stick to
> > exactly the same start & finish shown by parted.
> > 
> > Re-formatting it ought to be OK though, as long as the fat16 shown by
> > parted is correct.
> 
> I think filesystems other than FAT are aligned well already, assuming
> your partitions are aligned, but with FAT there are some hoops you
> must jump through.
> 
> There is a tool called flashbench that can test your drive
> (destructively!) and figure out the most optimal block sizes. Here's a
> great article about it and optimizing USB flash drives in general:
> https://lwn.net/Articles/428584/
> 
> And here is a forum thread about figuring out the FAT alignment:
> http://www.patriotmemory.com/forums/showthread.php?3696
> 
> The SD council makes a tool for MS Windows that optimally formats and
> securely erases SD cards. Might be interesting to compare the results
> of its format to a standard fdisk and mkfs.vfat in linux.
> 
> One thing I'm going to do next time I get a new SD card or flash drive
> is take a snapshot of the boot sector/partition tables/FAT tables so
> if I ever want to reformat it to FAT, I can restore the -- presumably
> optimal -- factory layout.

Excellent find!  I've got some studying to do. 

Thanks for sharing.  :-)
-- 
Regards,
Mick

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Re: [gentoo-user] Strange partition on USB stick

[Klaus Müller]

Am 04.10.11 00:15, Mick wrote:
> I can't recall if I asked this before, but I am looking at a partition on a 
> USB stick which seems to have a FAT16 fs on it and in parted says:
> 
> ==================================================
> Model: Crucial Gizmo! overdrive (scsi)
> Disk /dev/sdb: 1023MB
> Sector size (logical/physical): 512B/512B
> Partition Table: loop
> 
> Number  Start  End     Size    File system  Flags
>  1      0.00B  1023MB  1023MB  fat16
> ==================================================
> 
> What does "Partition Table: loop" mean?
> 

http://www.mail-archive.com/parted-devel@lists.alioth.debian.org/msg02423.html