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Special Forums Hardware Filesystems, Disks and Memory Slow copy (cp) performance when overwriting files Post 302831993 by jim mcnamara on Friday 12th of July 2013 11:09:22 AM
Old 07-12-2013
Also consider that
IF:
directory has large numbers of entries - >40K (varies with filesystem type)

Cure: make a directory tree, with each subdirectory having way smaller numbers of files.

Overly full disks can result in fragmented files which trashes update (cp overlay) performance of larger files.

So: You can experience lots of delay finding and overwriting files.

Another cause is poor inode caching. This is OS specific, I cannot comment specifically. But when you try to find a file in a directory, the kernel checks the inode cache first. If it finds the file in the cache it can open the file right away without having to scan thru a huge directory. inode caching also impacts the efficiency of PATH searching.
 

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xfs_ncheck(8)                                                 System Manager's Manual                                                xfs_ncheck(8)

NAME
xfs_ncheck - generate pathnames from i-numbers for XFS SYNOPSIS
xfs_ncheck [ -i ino ] ... [ -f ] [ -s ] [ -l logdev ] device DESCRIPTION
xfs_ncheck with no -i arguments generates an inode number and pathname list of all files on the given filesystem. Names of directory files are followed by /.. The output is not sorted in any particular order. The filesystem to be examined is specified by the device argument, which should be the disk or volume device for the filesystem. Filesystems stored in files can also be checked, using the -f flag. OPTIONS
-f Specifies that the filesystem image to be processed is stored in a regular file at device (see the mkfs.xfs -d file option). This might happen if an image copy of a filesystem has been made into an ordinary file. -l logdev Specifies the device where the filesystem's external log resides. Only for those filesystems which use an external log. See the mkfs.xfs -l option, and refer to xfs(5) for a detailed description of the XFS log. -s Limits the report to special files and files with setuserid mode. This option may be used to detect violations of security pol- icy. -i ino Limits the report to only those files whose inode numbers follow. May be given multiple times to select multiple inode numbers. If the filesystem is seriously corrupted, or very busy and looks like it is corrupt, a message of the form that would be generated by xfs_check(8) may appear. xfs_ncheck is only useful with XFS filesystems. SEE ALSO
mkfs.xfs(8), xfs_check(8), xfs(5). xfs_ncheck(8)
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