Hi, I have a problem with my JFS partition and I have a couple of questions.
After an unclean unmount and a restart a couple of files have been
truncated to size 0.
I am running linux 2.6.23.
I would really appreciate any help I can get, and I apologize for the huge
amount of questions :)
What could be the reason for these 0 sized files? Could a logredo be the
reason for this or a fsck?
Could jfs_logdump tell me anything interesting and if so what should I be
looking for?
>From what I understand JFS does not actually write the log to disk when a
transaction is committed. Is this right? And if so, where is the log stored
until it is written to disk, and does jfs_logdump show me the log on disk
or the log currently buffered somewhere?
The word "buffer" is used in a lot of places regarding the jfs log but I
have not found any actual definition of where this buffer is located or how
big it is or when it is flushed to the disk. One example taken from "JFS
Log" paper:
"In txCommit(), the tlck's are processed and log records are written (at
least to the buffer). The affected inodes are "written" to the inode extent
buffer (they are maintained in separate memory from the extent buffer).
Then a commit record is written".
Then it says:
"After the commit record has actually been written (I/O complete), the
block map and inode map are updated as needed, and the meta-data pages are
marked 'homeok'."
Why is the block and inode maps updated After the commit record is written,
isn't that information important to the transaction? And what does
meta-data "pages" refer to in this context? Are the log records called
pages, and are they located on disk or in memory?
What I don't understand is when and in what order the log records are
written to disk. My current theory is that the "buffers" related to the
files that become empty never is written to disk and when my system reboots
without unmounting the partition properly the meta-data-changes, (related
to the size of the file) are lost.
Is there any way of preventing this from happening in the future.
Best regards
Mikael Liljeroth
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