Eliot Moss via Cygwin wrote:
On 1/15/2023 3:38 AM, Christian Franke via Cygwin wrote:
Eliot Moss via Cygwin wrote:
I have a separate drive mounted this way:
d:/ /cygdrive/d ntfs binary,posix=0,user,noacl,auto 0 0
One thing I use it for is to store backup files. These tend to be 2 Gb
chunks, and there can be hundreds of them in the backup directory.
(The drive
is 5Tb.) The Windows Disk Management tool describes it as NTFS,
Basic Data
Partition.
Doing ls (for example) takes a very perceptible numbers of seconds
(though
whatever takes a long time seems to be cached, at least for a while,
since a
second ls soon after is fast).
The problem is the 'noacl' mount option and the fact that POSIX only
offers the *stat*() functions to retrieve file information. These
functions always need to provide the full file information, even if
only a small subset is needed.
To determine the 'x'-permission bits in the 'stat.st_mode' field on a
'noacl'-mount, Cygwin reads the first bytes of most files (all except
*.exe, *.lnk, *.com). The 'x' bits are set if the file starts with
"#!" (script), ":\n" (?) or "MZ" (Windows executable).
On 'noacl' mounts, this behavior could be suppressed by 'exec' or
'noexec' mount options.
Interesting. I removed the noacl from /etc/fstab and restarted all
Cygwin processes.
The mount program now shows that drive without noacl. It still takes
surprisingly
long to ls if I have not done so recently. The directory contains
~1200 files.
This depends on storage device, sometimes (HDD) on filesystem
fragmentation and always on 'ls' options. Plain '/bin/ls' without any
arguments does not call stat(). 'ls -s' or 'ls --color=yes' call stat()
for each file. 'ls -l' additionally calls getfacl() for each file if on
an 'acl' mount. The latter is apparently slower than expected, see below.
Here a quick test on a directory with 10000 ~3KB files on a NTFS USB
drive connected via USB-2 (~28MB/s raw read speed). The first test of
each mount variant was done immediately after connecting the drive:
$ TIMEFORMAT='%R'
1. mount [-o acl]
$ time ls -l > /dev/null
4.282
$ time ls -l > /dev/null
1.322
$ time ls -s > /dev/null
0.404
$ time ls > /dev/null
0.032
2. mount -o noacl
$ time ls -l > /dev/null
13.452
$ time ls -l > /dev/null
0.789
$ time ls -s > /dev/null
0.764
$ time ls > /dev/null
0.033
3. mount -o noacl,noexec
$ time ls -l > /dev/null
3.215
$ time ls -l > /dev/null
0.368
$ time ls -s > /dev/null
0.355
$ time ls > /dev/null
0.032
--
Regards,
Christian
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