On Wed, 24 Nov 2004 00:15:17 -0400, (e-mail address removed) (Paul) wrote:
Do you have any thoughts on whether the 137Gb barrier should be a
problem when the 160 Gb disk is partitioned into smaller 40/120
partitions?
watch this space
blackbat /\x/\
The barrier works like this:
An address can be 26 bits or 48 bits.
If the path to the hardware is limited to 26 bits, then
when you get to the 128GB mark, this is what happens to
the address
What_software_wants What_hardware_gets
(via 26 bit address)
0x03FFFFFE hex 11 1111 1111 1111 1111 1111 1110
0x03FFFFFF 11 1111 1111 1111 1111 1111 1111
0x04000000 00 0000 0000 0000 0000 0000 0000 !!!
Notice how the value the software is using, only
the lower 26 bits have a clear path to the hardware, on a
non 48bit LBA hardware device. When you try to write the sector
just above the 128GB mark, sector 0 gets zapped by the write
instead. The address appears to have "rolled over". Some
very key data on the disk will be killed.
That is why I advocate filling the disk with files, because the
partition that contains disk address 0x04000000 is the partition
that is going to kill the file system, when a file is written
into that spot or to a higher address. It doesn't matter how
many partitions you make, any of the partitions above 128GB
will result in disk data near 0x00000000 getting stomped on.
If you artificially avoid using the disk above the 128GB mark,
then it might be safe, but I would want a mechanism in the
disk itself, to exclude accesses to greater than the 128GB mark.
Either that, or get proper 48 bit support via a good PCI controller
card and the right Service Pack for the OS.
If you can fill the partition that contains the 128GB mark with
data, without the file system being corrupted, then your path to
the hardware must now be 48bit ready. By doing the test now
with dummy data files, you find out before any valuable data
is on the drive, whether everything is working. (I like to fill
all the partitions, so I know the whole disk works from the
hardware perspective. How much care you take with this,
really depends on how often you backup your data. If you do
daily backups, then you have hardly anything to lose - just
one day's accumulated data.)
HTH,
Paul