Reformatting SCSI disk sector size

By: Doug S (foo.delete@this.bar.bar), May 6, 2021 11:30 am
Room: Moderated Discussions
rwessel (rwessel.delete@this.yahoo.com) on May 6, 2021 9:32 am wrote:
> James (no.delete@this.thanks.invalid) on May 6, 2021 2:36 am wrote:
> > Etienne Lorrain (etienne_lorrain.delete@this.yahoo.fr) on May 6, 2021 1:08 am wrote:
> >
> > > I do not think there is any advantage in an "ECC line size" bigger than a very few hundred bytes (and
> > > there is disadvantages like latency)
> >
> > That was one of the big advantages Western Digital claimed
> > back when 4K disk blocks were first being introduced:
The
> > principle (sic) problem here is that ECC correction takes
> > place in 512B chunks, while ECC can be more efficient
> > when used over larger chunks of data. If ECC data is calculated
> > against a larger sector, even though more ECC
> > data is necessary than for a single 512B sector, less ECC
> > data than the sum of multiple sectors is needed to
> > maintain the same level of operational reliability. One estimate
> > for 4K sector technology puts this at 100 bytes
> > of ECC data needed for a 4K sector, versus 320 (40x8) for
> > 8 512B sectors. Furthermore the larger sectors means
> > that larger erroneous chunks of data can be corrected (burst
> > error correction), something that was becoming harder
> > as greater areal densities made it easier to wipe out larger parts of a 512B sector.
>
>
> I don't know enough about modern hard disk track formats, but historically, inter-block-gaps tended to scale
> more poorly than bits. IOW, if you doubled the linear bit density, you'd typically see less than a halving
> of the IBG, leading to more and more of the track being dedicated to IBGs. Going to a larger block size would
> help on that front too. If nothing else, the replacement of eight IBGs with one would be beneficial.


Yes I thought this was one of the main reasons for the increase in density. I remember back in the 90s it was possible to reformat SCSI disks with a larger sector size, and HP-UX handled that well so it was not terribly uncommon to do so to gain ~10% more space. IIRC the gain from 512B to 1K was something like 7%, with diminishing returns going to 2K and 4K (as you'd expect since you are knocking out fewer IBGs with each subsequent increase)

I have no clue whether reformatting those 90s SCSI disks with larger sectors also resulted in smaller / more efficient ECC calculations as above, or the gain was solely from the reduction in IBGs.
< Previous Post in ThreadNext Post in Thread >
TopicPosted ByDate
4K pages probably used to be too largeYuhong Bao2021/05/01 01:01 PM
  HDD seek time isn't freeMark Roulo2021/05/01 02:12 PM
    HDD seek time isn't freeYuhong Bao2021/05/01 02:21 PM
      HDD seek time isn't freeTim Mc2021/05/01 02:42 PM
        HDD seek time isn't freerwessel2021/05/01 02:57 PM
  4K pages probably used to be too largeBen LaHaise2021/05/02 10:45 AM
    VAX was 512 (in 1977) (NT)anonymous22021/05/02 08:36 PM
      FWIW, S/370 offered a choice of 2K and 4K (NT)rwessel2021/05/03 05:09 AM
      DEC's earliest PDP-11 disks were 512 (in 1971)John Yates2021/05/03 01:53 PM
    4K pages probably used to be too largeanon22021/05/03 01:17 AM
      4K pages probably used to be too largeBen LaHaise2021/05/03 05:36 PM
        Morotola 680x0 series page sizesBen LaHaise2021/05/03 05:51 PM
        4K pages probably used to be too largeanon22021/05/03 06:39 PM
          4K pages probably used to be too largeanon22021/05/03 08:51 PM
        4K pages probably used to be too largeYuhong Bao2021/05/03 10:51 PM
      4K pages probably used to be too largewumpus2021/05/05 09:06 AM
        4K pages probably used to be too largeanon22021/05/05 04:04 PM
          4K pages probably used to be too largeChester2021/05/05 06:45 PM
            4K pages probably used to be too largewumpus2021/05/06 09:06 AM
              Phenom TLB bugHeikki Kultala2021/05/06 12:46 PM
                Phenom TLB bugChester2021/05/06 05:29 PM
        4K pages probably used to be too largeEtienne Lorrain2021/05/06 01:08 AM
          4K pages probably used to be too largeJames2021/05/06 02:36 AM
            4K pages probably used to be too largerwessel2021/05/06 09:32 AM
              Reformatting SCSI disk sector sizeDoug S2021/05/06 11:30 AM
        4K pages probably used to be too largeDavid Hess2021/05/11 08:57 AM
  Page size is more complex/nuancedPaul A. Clayton2021/05/08 10:03 AM
Reply to this Topic
Name:
Email:
Topic:
Body: No Text
How do you spell tangerine? 🍊