🚀 go-pugleaf

In <2017@brchh104.bnr.ca> eap@bu-pub.bu.edu (Eric A Pearce) writes:

| I would *welcome* any corrections you have.
| 
| Most systems available today use the SCSI "Group 0" command set.  It has
| only 21 bits to store the absolute block number for a disk block.  This
| means you have a maximum of 2097152 (2^21) for the number of blocks you
| can address, which implies a maximum disk space of 1.073 gig (512k disk
| block * 2097152) .   There is a newer SCSI command set (extended SCSI)
| which allows 31 bits for the block number, but this doesn't seem to be
| currently available from Sun, Dec or SGI.  Neither Sun nor SGI were able
| to say anything definite about a new driver.

I don't speak for Sun or DEC, but SGI has been using the extended form of
the SCSI read and write commands ever since the 4D series of machines
started shipping 3 years ago.  No updated driver is required.  Group 1
commands aren't exactly *new*, you know.

| I haven't heard what happens on the SGI, but they do not
| currently support anything bigger than 1.2 gig, and their format typically
| eats 20% of the disk, so the problem isn't likely to occur with this
| drive.  (I don't have hard experience with this)

If you don't have any experience, why are you saying anything?  The 1.2Gb
is *unformatted* capacity.  Depending on the drive manufacturer, this is
anywhere from just over 21 bits to a fair bit more.  The exact amount over
21 bits depends partly on your sparing scheme and sector size, but will be
quite similar for any vendors platform.  Clearly, if you are using 1K
sectors, you don't have to worry until after 2Gb; if you are using 256
byte sectors for some strange reason, then you have a problem at .5 Gb.

	Dave Olson