Maximum Additional Partitions

JOJO jojo at
Mon Jan 29 11:51:23 PST 1996

* From the SCSI Reflector, posted by:
* JOJO <jojo at>
DOUG.PIRIE writes:
>* From the SCSI Reflector, posted by: 
> Medium Partiton page
> --------------------
> While the capacity and number of partitions may be determined by the medium 
> type and data format type for QIC drives it is not true for all tape devices. 
> DAT drives in particular will physically format the tape based on values 
> supplied by the host in the Medium Partition page.  In this case it is not the
> medium type which determines the number or size of the partitions and 
> therefore partitioning is not a medium attribute.
> I am not sure what you mean by the sentence," As it is now it is not possible 
> to determine the maximum number of partitions allowed by the medium?" If the 
> QIC-5010 spec. is similar to other QIC specs. then the number of and size of 
> partitions is fixed and unalterable by the host. If this is the case, then 
> maybe you know the max. number of partitions because you have read the data 
> format type on the tape.  
> ....

Hallo, again,

Thank you very much for a (very) prompt response to my inquiry! Here
are some additional notes and clarifications.

Medium Partition Page

I am still not quite happy with the definition of the "Maximum Additional
Partitions" field in the Medium Partition Page(1). Here is the reason why.
Some of the QIC tape spesifications allows partitioning of the media. This
means that while some tape formats can only have a single partition (no 
partitioning), others (the ones that allows partitioning) can have
more than one partition. In some cases both the number and size of each 
partition can be set by the host (through a MODE SELECT operation). In 
particuar, the QIC-5010 specification allows the medium to have from 1 
up to 36 partitions. The actual number of partitions and their sizes can be
set by the host. When a drive/logical unit is presented with an instance of 
such a medium both the maximum number of partitions and the actual number 
of partitions are determined by the currently loaded medium (the loaded 
medium holds information in addition to user data that describes the 
structure of the date (the partitioning)). This means that when such a tape 
is inserted into the drive, the drive actually has to inquire the medium to 
know how it is partitioned (both the number and size of each partition). The 
maximum number of partitions allowed however is (implicitely) given by the 
tape format standard (the density code). In this case (QIC-5010) the maximum 
number of partitions is 36 while for other tape formats the maximum may be 
any other number (1 or 2 for QIC tapes). The maximum number of partitions is
not known until a partitical medium has been loaded.

This leads to a situation where medium partitioning parameters (the actual
number of partitions, the maxium number of partitions allowed and the size
of each partition present on a partiticular instance of a medium) are all 
determined by the medium currently loaded (they are media attributes). 
In our case the tape drive itself does not impose any restrictions on these 
parameters (there is no maximum additional partitions limit imposed by the 
drive/logical unit).

By stating "as it is now it is not possible to determine (by a MODE SENSE
command) the (actual) maximum number of additional partitions (except
implicitely through the Density Code)", I am indicating that it seems to be
more natural (on a removable medium device such as ours) that the "Maxium 
Additional Partitions" indicates the actual limit as imposed by the medium 
currently loaded (and possible also the logical unit if it imposes additional
limitations). Otherwise a situation arises where "Maximum Additional 
Partitions" may have a value like 35 while with the medium currently loaded
the maximum is actually only 1.

Best regards,
Jorgen Johanson

Jorgen Johanson            jojo at
P.O Box 134 Kjelsas
N-0411 Oslo, NORWAY

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