[LU-13482] add verbose stats to lfs_migrate and "lfs migrate"

Related — Fri, 30 Jun 2023 00:35:03 +0000

It would be useful to add progress stats to "lfs_migrate" and "lfs migrate" with an option like "--verbose=stats" or "--stats" or similar. The time interval might be specified (e.g. "--stats-interval=N", but should default to once per 5s or so). This option should be passed through from "lfs_migrate" to "lfs migrate".

It is not possible/practical to show a "percent completion" bar for "lfs_migrate", since the number of files and their size is not practical to know in advance, but it should definitely be possible for "lfs migrate" to show the percent completion metric for migrating individual files, if they are taking a longer time to complete (not for every file if it is small, unless --verbose is used and the filename would be shown anyway).

For "lfs migrate" it can show something like the following in YAML format, so that it is also possible to parse this output for consumption by other tools:

filename:
- { seconds: <seconds>, rmbps: <MiB/s>, wmbps: <MiB/s>, copied: <MiB>, size: <MiB>, pct: <done>% }

Whether the status update line ends in a newline "\n" for logging or piped to another program, or only a carriage return "\r" (that overprints the previous line for more user-friendly output) can be determined by calling isatty. The seconds: field is the total elapsed time. The rmbps: (bytes read over read time) and wmbps: (bytes read over write time) values would be a decaying average data transfer rate across files if a single invocation is migrating multiple files, since small files would barely have time to print anything before they are completed, so the instantaneous transfer rates may not be very useful. copied: is the total number of bytes written for the current file, and size: is the total file size, pct: = copied/size.

For "lfs_migrate" what can be shown is the elapsed time and current decaying average values for total volume/rate of data migrated, number/rate of files migrated. Since this output will be intermingled with the "lfs migrate" output for each file, it makes sense to format it in a similar YAML style so that the full log is still readable, but it can be easily distinguished between what is global progress and what is per-file progress. The lfs_migrate script can use test -t 0 to determine if it is writing to a terminal or a log file, and whether the linefeed \n or carriage return \r is used at the end of line:

directory:
- { tot_sec: <seconds>, tot_files: <count>, avg_fps: <files_per_sec>, avg_rmbps: <MiB/s>, avg_wmbps: <MiB/s>, tot_size: <MiB> }

tot_sec: is the total elapsed time for the current migration, tot_files the total number of files (all entries) migrated so far, and avg_fps = tot_files/tot_sec for all files migrated so far. The totals line would only be shown every stats_interval seconds.

Whamcloud Community JIRA

[LU-13482] add verbose stats to lfs_migrate and "lfs migrate"