mount and umount large capacity external USB HDD (fstab)

[Julian Elischer]

>> I believe there are 2 limits you may be encountering.  The disk is larger
>> than 2TiB and is low-level formatted with 4096 bytes sectors.  The 2TiB
>> limit results from clculations with 32 bit integers and 512 byte sectors.
>>
>> The large sector size is almost certainly the problem with "dd"...you
>> can read less than a sector, but an attempt to write less than a sector
>> will fail.  Try bs=4k.
>>
>> I'm running 8 Stable as of a few days ago.  The "fdisk" sources on
>> this system were updated 11/22/2010, but appear to handle sector sizes
>> only
>> up to 2048 bytes.  I haven't checked to see if it handles disk or
>> partition
>> sizes above 2TiB, but it doesn't matter, it won't handle your disk
>> properly,
>> and I doubt that the FBSD 7.3 fdisk would either.  There is no option for
>> sector size, it's a hard-coded limit which is too small.
>>
>> Bsdlabel may have similar limits.  The version on this system was last
>> modified 09/26/2010.  It reads the sectorsize from the disk and therefore
>> should have no trouble with a 3tb disk.  I don't know whether the 7.3
>> fdisk has these modifications, but with fdisk failing, it doesn't matter.
>> If you are using the disk only under freebsd you might try using
>> 'bsdlabel'
>> on the entire disk (da0), but check I suspect your bsdlabel may not be
>> upgraded yet (check sbin/bsdlabel).
>>
>> The manual page for 'gpart' claims that it was introduced in 7.0, and I
>> would think it would be working reasonably by 7.3.  It should be able
>> to handle large disks and partitions with no trouble, and is much easier
>> to use than the old stuff.  You said in your last email that 'gpart show'
>> showed nothing, but that may be because it had nothing intelligible to
>> show.  If you haven't tried it yet, and the disk contains no data which
>> you might lose, then try the recipe from the link I gave you.  Create
>> a couple of partitions, then try 'gpart show'.
>>
>> Alternately, you may try getting recent versions of fdisk and bsdlabel
>> from cvs or svn, increase the sector size limit in fdisk, and try that
>> route again.
>>
>> --
>> Duane H. Hesser
>>
> Thank you all for your input.  We must admit, we have a bit more reading
> to do to fully understand what "Nagilum" was providing.  On the other
> hand, we do understand more of what Mr. Hesser was saying, however, we
> aren't prepared to upgrade to to 8.x or start playing around by
> replacing/updating individual utilities on this 'live 7.3 system'.
> Perhaps on a test machine 'first'.  Until then we will have to take the
> whimp way out and format the 3TB USB device with NTFS and mount it until
> we are better versed on exactly where Freebsds' support is for these HDD's
> that are greater than @-TB in size.
>
> We really would like at least one (1) FreeBSD machine that is all,
> dedicated so to speak, BSD.
>
> We will read that recipe.  Should anyone make additions to this thread we
> are all eyes_&_ears.
>

As was mentioned before, the limitationcomes from the defintion of the 
partition
structures. Firstly the fdisk structure introduced with the IBM PC  (I 
think) has onlt room for
32 bits on its sector tables. secondly the bsd  'label' structure 
introduced
in the 80s has a similar limitiation.
The new structure to get around this is the GPT structure. you need to 
partition
the drive with a gpt  capable partitioning tool..  gpart claims to do 
this (though
I have never done it as I don't have a need (yet)). This limitiation 
will affect
any system which you wil use to write those partition types and is 
indepenent
of file system.  In addition Once you have made a partition big 
enough, you
will need to populate it wirth a filesystem capable of representing 
data to that scale.
UFS2 and ZFS are two candidates for this.

If you take a modern Windows, it will probably partitionthe drive 
using a GPT table
or some similar modern structure.(I don't have any modern windows 
system so I can't tell
you exactly what they do, but they MUST have done the same thingif 
they didn't use GPT itself.)
This is  a separate step from puting the file system on, though the 
windows tools may
present it as a single step.

I hope y'all will find this useful.


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