You're right about ODS-1, I mis-remembered that: > he logical block containing the home block is the > first good block on the volume out of the sequence 1, 256, > 512, 768, 1024, 1280, .... 256*n. ODS-2:
The home block search delta is computed from the geometry of the volume such that# if the volume is viewed as a three di- mensional space# the search sequence will travel approxi- mately down the body diagonal of the space. Since volume failures tend to occurr across one dimension# this minimizes the chance of a single failure dest-rovi ng ' bot h home blocks of the volume. The search delta is eomouted from the volume geometry, expressed in sectors# tracks (surfaces)# and cyl- inders# according to the following rules# to handle the cases where one or two dimensions of the volume have a size of 1, In most cases# the home block is located on L8N 1, The question, and what I'm working on, related to ODS-2 On 03-Mar-16 11:25, 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... Johnny > _______________________________________________ Simh mailing list > [email protected] > http://mailman.trailing-edge.com/mailman/listinfo/simh
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