storage: possibly incorrect use of Bsize instead of Frsize in sysutil.StatFS

[stevendanna]

Describe the problem

In sysutil.StatFS we return the Bsize field as the "BlockSize":

cockroach/pkg/util/sysutil/sysutil_unix.go

Line 52 in dac79a2

BlockSize: int64(fs.Bsize),

cockroach/pkg/cli/debug.go

Line 243 in dac79a2

free := fs.AvailBlocks * fs.BlockSize

Unfortunately, on Linux, I believe that the frsize field should be preferred over bsize when calculating total sizes from statfs output. While counterintuitive based on their plain-language descriptions, the authors of GNU coreutils and gnulib seem to agree. The issue here: cockroachdb/pebble#1072 provides an example of the potential problem.

Jira issue: CRDB-3055

[jbowens]

This is also potentially a problem with the capacity calculations that power the capacity timeseries metric (and rebalancing decisions). Currently, we use the github.com/elastic/gosigar module for this purpose:

cockroach/pkg/storage/mvcc.go

Line 3735 in 8be5c15

if err := fileSystemUsage.Get(dir); err != nil {

https://github.com/elastic/gosigar/blob/v0.14.1/sigar_unix.go#L23

[github-actions]

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