> On Apr 21, 2024, at 1:37 PM, Robert Ayrapetyan <robert.ayrapetyan@xxxxxxxxx> wrote:
>
> Hello!
>
> Attempting to understand the implementation of server-side copying of
> folders mounted via NFS 4.2.
> Currently copying an entire folder (cp -r --reflink=always) produces:
>
> newfstatat(AT_FDCWD, "/mnt/source_file", {st_mode=S_IFREG|0644,
> st_size=2466, ...}, AT_SYMLINK_NOFOLLOW) = 0
> newfstatat(3, "dest_file", {st_mode=S_IFREG|0644, st_size=2466, ...}, 0) = 0
> openat(AT_FDCWD, "/mnt/source_file", O_RDONLY|O_NOFOLLOW) = 4
> newfstatat(4, "", {st_mode=S_IFREG|0644, st_size=2466, ...}, AT_EMPTY_PATH) = 0
> openat(3, "dest_file", O_WRONLY|O_TRUNC) = 5
> ioctl(5, BTRFS_IOC_CLONE or FICLONE, 4) = 0
> close(5) = 0
> close(4)
>
> sequence of operations for each file within the directory on the
> client side. Notably, the actual file copy occurs on the server side
> and is instantaneous (BTRFS_IOC_CLONE).
> But for TTLs around 50 ms (such as within intra-regional connections
> like US West/East), copying a 700MB directory containing 500 files
> takes about 4 minutes (while "true" server-side folder copy is almost
> instant).
>
> Exploring if there exists a Linux mechanism enabling the copying of an
> entire folder without individually accessing each file within the
> directory for server-side copy operation.
The Linux FS community has discussed this issue in the
past.
The usual approach is to teach the user space utilities
(tar, rsync, and the like) to kick off file copies in
parallel.
--
Chuck Lever
