[Info-vax] Out of diskspace :(

[hb]

On May 19, 5:38 pm, Johnny Billquist <b... at softjar.se> wrote:
> I would not expect VMS home blocks to be located on different blocks
> depending on the size of the disk. You learn something every day.

Usually the home block is in the second logical block: LBN 1. This LBN
is called the primary home block. If the primary home block is not
found (corrupted or overwritten by whatever), secondary home blocks
are searched at different LBNs of the disk. The secondary home block
LBNs are derived from the size of the disk. This is called the
secondary home block search sequence.

ODS2/5 for OpenVMS/I64 uses a GPT (GUID Partitioning Table ) which
occupies at least LBN 0 and 1. So there are no primary home blocks for
these disks.

Also, according to the "VMS File System Internals" book, the file
system must be able to allocate two good home blocks. It's not
explained how the second good home block is found. Home blocks are in
the VBNs 2,...,cluster_factor*3 of INDEXF.SYS. For a valid home block
in LBN 1 one could get another home block from INDEXF.SYS without
depending on the disk size. But it seems the file system rather looks
for another good home block on the search sequence than trusts what it
finds at LBN 1, which makes sense to me and which may explain "not
finding the home block" after the disk size changed.