Doug Siebert (foo@bar.bar) on 9/22/08 wrote:
---------------------------
>Way back in the mid 90s or so I experimented with the low SCSI commands that let
>you reformat drives with larger sector sizes, and found that I gained something
>like 7% going to 1K sectors, and I think it was 13% going to 4K sectors, which was
>the largest that drive would allow (IIRC it was a 2GB Seagate)
>
>I never had the guts to actually use it that way though, even though back then
>an extra 13% of hard drive space was not be sneezed at (in today's world of super-cheap
>1TB drives, I'm afraid I would sneeze at it...) Although I was able to format a
>filesystem on that drive under HP-UX and it appeared to work normally, I figured
>there was going to be something that would break somewhere that would make me regret
>it, so I formatted it back to 512 byte sectors.
>
>So now they are finally going to do it, just when few people really need that extra space!
>
>Have they resolved all the issues with having more than 2^32 sectors for SCSI?
>For SATA? This would limit drives to 2TB when using 512 byte sectors. I suspect
>there are still some problems out there (or too many older versions of OS still
>in common use that couldn't use drives with more than 2^32 sectors) so we'll see
>4K sectors just to push out the day of reckoning a few years.


I'm not 100% sure what will break more code - disks with more than 2**32 sectors, or sectors bigger than 512 bytes. But I'd bet on the latter. There are, after all, already many systems with volumes bigger than 2**32 sectors, and almost no (mainstream) systems using volumes with sectors bigger than 512 bytes. For reference, Win2K and later all support 48-bit LBA and large volumes already (although for 48-bit LBA support a service pack* is required for Win2K and XP, and in the case of Win2K a registry setting is required). And of course Linux support is there as well.

As for hardware, BIOSs and whatnot, again, you'll have issues on both fronts. Shades of the many BIOS/DOS/FAT/ST-506/IDE/ATA/whatever limits we've seen over the years. And there again, you're probably looking at a bigger problem with 4KB sectors. Essentially all SATA HBAs and BIOSs *should* support 48-bit LBA already, but there will undoubtedly be some bugs showing up. And current PATA hardware and BIOSs ought to support 48-bit LBA, but much older hardware exists that does not.

But I'd expect the issues in either case to be relatively small.

And frankly, larger sectors ought to be an option on most drives, since 512 bytes is pretty darn small these days, and as other have pointed out, many OSs invariably do I/O in bigger chunks anyway. OTOH, reading or writing several consecutive sectors isn't really that big an imposition, if you're willing to give up a big of disk space.

Actually this was tried before - in the days when disk sizes started bumping past the 32MB FAT16 limit, a number of people did device drivers that faked larger sectors. It wasn't pretty.


*quite old SPs.