ISC 2.2.1 + Fujitsu 1.2Gb drive + AHA 1740 EISA SCSI

[Thomas Hoberg]

In article <1991May01.114725.14859 at virtech.uucp>, cpcahil at virtech.uucp (Conor P. Cahill) writes:
|> cm at jet.uucp (colin manning) writes:
|> >The Fujitsu 2266 has 1029 cylinders. Although the fdisk table only
|> >caters for disks with up to 1024 cylinders, ISC's documentation says
|> >that it will use the additional cylinders, if you try to allocate
|> >them when partitioning the disk during installation. I had a mail
|> >msg some time back from someone who said that this does not work, and
|> >furthermore that by attempting to use cylinders >1024, the system will wrap
|> >around to cylinder 0 and clobber the start of your disk (which would
|> >be *serious*).
|> 
|> The wrap-around problem is not related to 1024 cylinders.  It is some 
|> function of disk size and as far as I know only happens on 1.2GB or 
|> higher drives.  Last I heard ISC knew about the problem and was working
|> on it, but that was months ago.  Perhaps it has been solved by now.
[...]

When using the Adaptec UNIX and any other OS care rather little about the
physical layout of the disk. The Adaptec will remap any SCSI drive to 32 sectors,
64 heads and as many cylinders as there is megabytes on the disk. This comes
rather handy when you are asked by 'fdisk'just how many cylinders you want to
allocate for a partition. This induces some latency due to the Adaptecs 8085
having to do some calculations, but with SCSI's defect management a sector might
not end up where you believe it should, anyway. With my 1.2GB I am still 'lucky',
because it only has about 970MB after formatting, meaning 970 cylinders. Once
you got a true 1.2GB drive you are in for trouble, because soft cylinder numbers
will actually exceed 1024. On the other hand huge ESDI drive with >1024 cylinders
can be made to work with ISC, so it's probably not a big deal to fix it. Until
then you will just have to forego some of your disks capacity.

-- tom 
----
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