[Info-vax] Support of partitioning

[Eberhard Heuser]

Am 03.05.2015 um 19:21 schrieb JF Mezei via Info-vax:
> It is well known that VMS doesn't support partitioning has has had to do
> some black magic to pretend to support it.
>
> How difficult is it for VMS to support partitioning ? What is involved
> in providing support ?
>
> >From the ODS point of view, isn't just a question of remapping blocks ?
>
> So for a 7000 block partition starting at physical block 2000, when ODS
> wants to access block 0, it gets remapped to read physical block 2000 ?
> Is that how it works ?
>
> I take it that at boot, the system would have to look at all physical
> drives to create virtual disk devices for each partition ?  Is that a
> big problem ?
>
> Are there performance issues with IOs first going to the virtual disk
> driver that works out the virtual disk block into physical disk blocks
> and then issues IO to the physical driver ? Or would the two be combined
> into the same code/driver ?
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The lddriver can do this:

$ type LD_lbn_share.COM
$ phdev := $9$dka400:
$ show dev 'phdev'
$ ld connect 'phdev' lda1:/log/lbn=(start=0,count=10000)/share/alloclass=4
$ ld connect 'phdev' 
lda2:/log/lbn=(start=10000,count=10000)/share/alloclass=4
$ ld connect 'phdev' 
lda3:/log/lbn=(start=20000,count=10000)/share/alloclass=4
$ ld connect 'phdev' 
lda4:/log/lbn=(start=30000,count=10000)/share/alloclass=4
$ mount/system lda1: test1
$ mount/system lda2: test2
$ mount/system lda3: test3
$ mount/system lda4: test4
$ show dev lda1
$ show dev lda2
$ show dev lda3
$ show dev lda4
$ show dev 'phdev'
$ inquire dummy "return to continue"
$ dismount lda1:
$ dismount lda2:
$ dismount lda3:
$ dismount lda4:
$ ld disconnect/log/all
$ show dev 'phdev'

$ ld version
%LD-I-VERSION, LD version V9.7, module X-12 built on Aug  7 2012 23:02:34

Eberhard