<html>
<head>
<meta content="text/html; charset=utf-8" http-equiv="Content-Type">
</head>
<body bgcolor="#FFFFFF" text="#000000">
You're right about ODS-1, I mis-remembered that:<br>
<blockquote type="cite">
<pre style="box-sizing: border-box; font-family: Monaco, Menlo, Consolas, 'Courier New', monospace; font-size: 13px; white-space: pre-wrap; display: block; padding: 9.5px; margin: 0px 0px 10px; line-height: 1.42857; word-break: break-all; word-wrap: break-word; color: rgb(51, 51, 51); border: 1px solid rgb(204, 204, 204); border-radius: 4px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; widows: 1; word-spacing: 0px; -webkit-text-stroke-width: 0px; background-color: rgb(245, 245, 245);">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.</pre>
</blockquote>
ODS-2:<br>
<pre style="box-sizing: border-box; font-family: Monaco, Menlo, Consolas, 'Courier New', monospace; font-size: 13px; white-space: pre-wrap; display: block; padding: 9.5px; margin: 0px 0px 10px; line-height: 1.42857; word-break: break-all; word-wrap: break-word; color: rgb(51, 51, 51); border: 1px solid rgb(204, 204, 204); border-radius: 4px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; widows: 1; word-spacing: 0px; -webkit-text-stroke-width: 0px; background-color: rgb(245, 245, 245);">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,
<img src="cid:part1.09060902.01090204@ieee.org" alt="">
In most cases# the home block is located on L8N 1,
</pre>
<pre class="moz-signature" cols="72">The question, and what I'm working on, related to ODS-2
</pre><div class="moz-cite-prefix">On 03-Mar-16 11:25, Johnny Billquist wrote:
</div><blockquote cite="mid:56D8657F.9060904@softjar.se" type="cite">On 2016-03-03 17:21, Timothe Litt wrote:
<blockquote type="cite">On 03-Mar-16 11:12, Johnny Billquist wrote:
<blockquote type="cite">What does the physical disk geometry have to do with Files-11?
At least ODS-1 couldn't care less.
Johnny
</blockquote>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.
</blockquote>
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
<a class="moz-txt-link-abbreviated" href="mailto:Simh@trailing-edge.com">Simh@trailing-edge.com</a>
<a class="moz-txt-link-freetext" href="http://mailman.trailing-edge.com/mailman/listinfo/simh">http://mailman.trailing-edge.com/mailman/listinfo/simh</a>
</blockquote>
</body></html>