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94 lines
3.8 KiB
94 lines
3.8 KiB
OCFS2 online file check
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-----------------------
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This document will describe OCFS2 online file check feature.
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Introduction
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============
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OCFS2 is often used in high-availability systems. However, OCFS2 usually
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converts the filesystem to read-only when encounters an error. This may not be
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necessary, since turning the filesystem read-only would affect other running
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processes as well, decreasing availability.
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Then, a mount option (errors=continue) is introduced, which would return the
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-EIO errno to the calling process and terminate further processing so that the
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filesystem is not corrupted further. The filesystem is not converted to
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read-only, and the problematic file's inode number is reported in the kernel
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log. The user can try to check/fix this file via online filecheck feature.
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Scope
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=====
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This effort is to check/fix small issues which may hinder day-to-day operations
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of a cluster filesystem by turning the filesystem read-only. The scope of
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checking/fixing is at the file level, initially for regular files and eventually
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to all files (including system files) of the filesystem.
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In case of directory to file links is incorrect, the directory inode is
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reported as erroneous.
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This feature is not suited for extravagant checks which involve dependency of
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other components of the filesystem, such as but not limited to, checking if the
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bits for file blocks in the allocation has been set. In case of such an error,
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the offline fsck should/would be recommended.
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Finally, such an operation/feature should not be automated lest the filesystem
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may end up with more damage than before the repair attempt. So, this has to
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be performed using user interaction and consent.
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User interface
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==============
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When there are errors in the OCFS2 filesystem, they are usually accompanied
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by the inode number which caused the error. This inode number would be the
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input to check/fix the file.
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There is a sysfs directory for each OCFS2 file system mounting:
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/sys/fs/ocfs2/<devname>/filecheck
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Here, <devname> indicates the name of OCFS2 volume device which has been already
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mounted. The file above would accept inode numbers. This could be used to
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communicate with kernel space, tell which file(inode number) will be checked or
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fixed. Currently, three operations are supported, which includes checking
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inode, fixing inode and setting the size of result record history.
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1. If you want to know what error exactly happened to <inode> before fixing, do
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# echo "<inode>" > /sys/fs/ocfs2/<devname>/filecheck/check
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# cat /sys/fs/ocfs2/<devname>/filecheck/check
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The output is like this:
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INO DONE ERROR
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39502 1 GENERATION
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<INO> lists the inode numbers.
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<DONE> indicates whether the operation has been finished.
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<ERROR> says what kind of errors was found. For the detailed error numbers,
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please refer to the file linux/fs/ocfs2/filecheck.h.
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2. If you determine to fix this inode, do
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# echo "<inode>" > /sys/fs/ocfs2/<devname>/filecheck/fix
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# cat /sys/fs/ocfs2/<devname>/filecheck/fix
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The output is like this:
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INO DONE ERROR
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39502 1 SUCCESS
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This time, the <ERROR> column indicates whether this fix is successful or not.
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3. The record cache is used to store the history of check/fix results. It's
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default size is 10, and can be adjust between the range of 10 ~ 100. You can
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adjust the size like this:
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# echo "<size>" > /sys/fs/ocfs2/<devname>/filecheck/set
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Fixing stuff
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============
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On receiving the inode, the filesystem would read the inode and the
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file metadata. In case of errors, the filesystem would fix the errors
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and report the problems it fixed in the kernel log. As a precautionary measure,
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the inode must first be checked for errors before performing a final fix.
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The inode and the result history will be maintained temporarily in a
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small linked list buffer which would contain the last (N) inodes
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fixed/checked, the detailed errors which were fixed/checked are printed in the
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kernel log.
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