On 2016-03-03 17:25, Johnny Billquist wrote:
On 2016-03-03 17:21, Timothe Litt wrote:
On 03-Mar-16 11:12, Johnny Billquist wrote:
What does the physical disk geometry have to do with Files-11?
At least ODS-1 couldn't care less.
Johnny
The home block search sequence - for both ODS1 and ODS2 - uses the
geometry to determine where the HOM blocks are located.
Usually block 1 is the primary HOM block. But the spec requires a
backup HOM block, and the search sequence varies based on the geometry.
It was an attempt to search in 3 dimensions to avoid probable media
damage scenarios. Think of each attempt as a rotation, move inward and
up. But there are special cases. Read the spec for details.
If a reader insists on finding the second (or subsequent) HOM block, it
can't without the geometry.
The geometry is also (sometimes) used for file placement, which a reader
shouldn't care about.
I should check, but I'm pretty sure the home block copies for ODS-1 is
at 256, 512, 1024... Logical block number. So not based on geometry at all.
But let me check later tonight, to be sure...
Just checked the ODS1 specification, and the home block is defined as
the first good block in the sequence 1, 256, 512, 768, 1024, 1280, ...,
256*n
Johnny
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