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Operating Systems AIX AIX System paramerter for Disk performance Post 302096752 by gogogo on Friday 17th of November 2006 08:11:34 PM
Old 11-17-2006
Is it the only direct way to fix the question?


File system buffer tuning
The following ioo and vmstat -v parameters can be useful in detecting I/O buffer bottlenecks and tuning disk I/O:

Counters of blocked I/Os due to a shortage of buffers
The vmstat -v command displays counters of blocked I/Os due to a shortage of buffers in various kernel components. Here is part of an example of the vmstat -v output:
...
0 paging space I/Os blocked with no psbuf
2740 filesystem I/Os blocked with no fsbuf
0 external pager filesystem I/Os blocked with no fsbuf

...
The paging space I/Os blocked with no psbuf and the filesystem I/Os blocked with no fsbuf counters are incriminated whenever a bufstruct is unavailable and the VMM puts a thread on the VMM wait list. The external pager filesystem I/Os blocked with no fsbuf counter is incriminated whenever a bufstruct on an Enhanced JFS file system is unavailable
The numfsbufs parameter
If there are many simultaneous or large I/Os to a filesystem or if there are large sequential I/Os to a file system, it is possible that the I/Os might bottleneck at the file system level while waiting for bufstructs. You can increase the number of bufstructs per file system, known as numfsbufs, with the ioo command. The value takes effect only when a file system is mounted; so if you change the value, you must then unmount and mount the file system again. The default value for numfsbufs is currently 93 bufstructs per file system.
 

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

NAME
xfs_freeze - suspend access to an XFS filesystem SYNOPSIS
xfs_freeze -f | -u mount-point DESCRIPTION
xfs_freeze suspends and resumes access to an XFS filesystem (see xfs(5)). xfs_freeze halts new access to the filesystem and creates a stable image on disk. xfs_freeze is intended to be used with volume managers and hardware RAID devices that support the creation of snapshots. The mount-point argument is the pathname of the directory where the filesystem is mounted. The filesystem must be mounted to be frozen (see mount(8)). The -f flag requests the specified XFS filesystem to be frozen from new modifications. When this is selected, all ongoing transactions in the filesystem are allowed to complete, new write system calls are halted, other calls which modify the filesystem are halted, and all dirty data, metadata, and log information are written to disk. Any process attempting to write to the frozen filesystem will block waiting for the filesystem to be unfrozen. Note that even after freezing, the on-disk filesystem can contain information on files that are still in the process of unlinking. These files will not be unlinked until the filesystem is unfrozen or a clean mount of the snapshot is complete. The -u flag is used to un-freeze the filesystem and allow operations to continue. Any filesystem modifications that were blocked by the freeze are unblocked and allowed to complete. One of -f or -u must be supplied to xfs_freeze. NOTES
A copy of a frozen XFS filesystem will usually have the same universally unique identifier (UUID) as the original, and thus may be pre- vented from being mounted. The XFS nouuid mount option can be used to circumvent this issue. In Linux kernel version 2.6.29, the interface which XFS uses to freeze and unfreeze was elevated to the VFS, so that this tool can now be used on many other Linux filesystems. SEE ALSO
xfs(5), lvm(8), mount(8). xfs_freeze(8)
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