Jay Daniels wrote:
What if any are the partition limits on scsi drives?
I have been setting up partition with linux fdisk, the first 3 being
primary partitions and all others inside one big extended partition -
commonly viewed with linux fdisk -l as Win95 Ext'd (LBA).
In otherwords, I setup scsi drives the same as ide drives.
Do scsi drives have this same partition limit as ide drives or is this
a limitation of the fdisk tool or system bios?
Essentially, LBA (and SCSI) make the disk look like a contiguous string
of "N" blocks, rather than IDE's native method of cylinder, head, sector
(or "CHS", a hold-over from the days of ST-506 or ST-412 MFM hard
drives).
The BIOS must be able to address all of the blocks. In other words, a
32-bit unsigned integer can address 2^32 or 4,294,967,295 blocks (2TB).
BTW, this is the difference between Windows' FAT-12 (12-bit value,
2MB), FAT-16 (16-bit value, 32MB), and FAT-32 (32-bit value, 2TB)
filesystems.
Other limits are inherent in library routines such as lseek(2). They
use a signed integer to seek around in a file. A signed 32-bit integer
will only allow direct access to 2^31 bytes (2GB) of data, hence the
file size limit unless you have your libraries compiled with "LARGEFILE"
support (where you get a signed long, 2^63 bytes or a really, really
large number!). Virtually all Linux stuff (well, gcc-compiled stuff)
use LARGEFILE, but you must make sure that the "offset" variable you
use is declared as
off_t offset;
as opposed to the classic
int offset;
which will stick you with the 2GB limit (remember, an "int" is the
"natural" size of the machine...32-bits on an x86).
Furthermore, why is an extended partition listed in Linux as a
"Win95" Ext'd (LBA)?
There's actually two types, type 5 (extended) and type f (win95 extended
LBA). I'm not absolutely certain what the difference is other than
type f is a FAT-32 LBA-addressed partition. I think type 5 is FAT-16
extended. I could be wrong there.
And now you know far more than you ever cared to! :-p
----------------------------------------------------------------------
- Rick Stevens, Senior Systems Engineer rstevens@xxxxxxxxxxxxxxx -
- VitalStream, Inc. http://www.vitalstream.com -
- -
- Linux is like a wigwam...no windows, no gates...and apache inside! -
----------------------------------------------------------------------
