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- file backend could have different dependencies

- default 1 second, each direction, before measurements

- default to 100

- may need some tweaks to confirm/correct which interface is used

- match current style on cooley and bebop
- set explicit HOME to avoid interference from user spack env

- must build benchmarks twice, once with pmdk back end and once with
  file backend
- rpath in executable keeps a fixed library linkage otherwise

- includes two bake builds: one with pmdk, one with file backend
- actual runs do not work yet due to a mount problem

- size of buffer to iterate over during transfer
- if this size matches transfer size, then a single hot buffer will be used
  repeatedly for all operations