* chunkd on-disk format update
@ 2010-07-04 6:08 Jeff Garzik
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From: Jeff Garzik @ 2010-07-04 6:08 UTC (permalink / raw)
To: Project Hail
A disruptive chunkd on-disk file format change was just pushed to
hail.git. It is a minor format update, but it is incompatible. chunkd
v0.8+ objects are now binary-incompatible with the just-released chunkd
v0.7.
The update adds a magic number and object size to the on-disk object
header (struct be_fs_obj_hdr), plus some reserved space for future
additions.
The magic number and object size add easy (and CPU-inexpensive) sanity
checks to the object I/O code. The object size field is largely
redundant, intended mainly for disaster recovery. However, storing the
object size enables the file format to support multiple objects inside a
single POSIX filesystem file.
Hopefully this means implementing an APPEND operation in chunkd is now
feasible. But if APPEND falls through, these two new be_fs_obj_hdr
members retain some utility anyway.
Jeff
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2010-07-04 6:08 chunkd on-disk format update Jeff Garzik
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