Citing Kerrisk, The Linux Programming Interface:
The O_NOATIME flag is intended for use by indexing and backup
programs. Its use can significantly reduce the amount of disk
activity, because repeated disk seeks back and forth across the
disk are not required to read the contents of a file and to update
the last access time in the file’s i-node[.]
restic used to do this, but the functionality was removed along with the
fadvise call in #670.
Currently, `restic backup` (if a `--parent` is not provided)
will choose the most recent matching snapshot as the parent snapshot.
This makes sense in the usual case,
where we tag the snapshot-being-created with the current time.
However, this doesn't make sense if the user has passed `--time`
and is currently creating a snapshot older than the latest snapshot.
Instead, choose the most recent snapshot
which is not newer than the snapshot-being-created's timestamp,
to avoid any time travel.
Impetus for this change:
I'm using restic for the first time!
I have a number of existing BTRFS snapshots
I am backing up via restic to serve as my initial set of backups.
I initially `restic backup`'d the most recent snapshot to test,
then started backing up each of the other snapshots.
I noticed in `restic cat snapshot <id>` output
that all the remaining snapshots have the most recent as the parent.
Currently restic copy will copy each blob from every snapshot serially,
which has performance implications on high-latency backends such as b2.
This commit introduces 8x parallelism for blob downloads/uploads which
can improve restic copy operations up to 8x for repositories with many
small blobs on b2.
This commit also addresses the TODO comment in the copyTree function.
Related work:
A more thorough improvement of the restic copy performance can be found
in PR #3513
Closes #3595
Choosing to include `stdoutIsTerminal()` as:
- all other instances with `!opts.JSON` do so
- this likely will not affect anything, especially when autorun
- this seems to not be a meaningful enough summary
to include in auto-backup reports
JSON is still likely not guaranteed to work and this is a suboptimal
solution to this. Ideally, #1804 should refactor all print statements,
and define+document(+handle) when stdoutIsTerminal() should be used.
Else, it may end up more inconsistent and bulky
(duplicate lines, longer files).
The keyfile provided by restic's own webserver (https://restic.net) should be
more stable than relying on public keyservers. So I changed the URL to the
GPG keyfile, as recommended by MichaelEischer.
