> > Low-level snapshots don't do any good, they just freeze the "halfway
> > there" on-disk structure.
>
> But [s|g]tar, cpio, afio (don't know about dsmc) also freeze the
> "halfway there" data, but at the file level instead (application
> instead of filesystem)...
Not if some day somebody implements file system level snapshots for
Linux. Until then, better have garbled file contents constrained to a
file than random data as on-disk layout changes with hefty directory
updates.
dsmc fstat()s the file it is currently reading regularly and retries the
dump as the changes, and gives up if it is updated too often. Not sure
about the server side, and certainly not a useful option for sequential
devices that you directly write on. Looks like a cache for the biggest
file is necessary.
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