[OpenAFS] Re: Questions regarding `afsd` caching arguments (`-dcache` and `-files`)

Ciprian Dorin Craciun ciprian.craciun@gmail.com
Fri, 8 Mar 2019 18:36:20 +0200

On Fri, Mar 8, 2019 at 6:19 PM Ciprian Dorin Craciun
<ciprian.craciun@gmail.com> wrote:
> (B)  Using `-files` and `-chunksize` so that their product is larger
> than `-blocks` means that the cache can hold up to as many `-files`
> actual AFS files, but their total size can't be larger than `-blocks`?
>  (I.e. if one has a cell with lots of small files, it is OK to
> configure a largish `-chunksize` and `-files` because they will be
> cached up to `-blocks`.)

I've found the http://docs.openafs.org/Reference/5/afs_cache.html
documentation that states:
Vn files expand and contract to accommodate the size of the AFS
directory listing or file they temporarily house. As mentioned, by
default each Vn file holds up to 64 KB (65,536 bytes) of a cached AFS
element. AFS elements larger than 64 KB are divided among multiple Vn
files. If an element is smaller than 64 KB, the Vn file expands only
to the required size. A Vn file accommodates only a single element, so
if there many small cached elements, it is possible to exhaust the
available Vn files without reaching the maximum cache size.

This would imply that:

* there is no 1-to-1 relation between "chunks" and "Vn files", one
chunk could be stored in multiple "Vn files";  (however one "Vn file"
never stores multiple chunks in case the chunk size is bellow 64K?)

* by explicitly setting `-files` one can set a limit to the maximum
number of actual AFS files to cache;  (i.e. if all files are smaller
than 64K and the `-blocks` is larger than `-files * 64K`, then no more
than `-files` AFS files would be stored;)

Am I correct?