Re: ext3 file system

Hans Reiser
2003-12-18T01:25:25Z

jshankar wrote:

>Hello,
>
>Please provide some more insight.
>
>Suppose a filesystem issues a write command to the disk with around 10 4K
>Blocks to be written. SCSI device point of view i don't get what is the
>parallel I/O.
>It has only 1 write command. If some other sends a write request it needs to
>be queued. But the next question arises how the write data would be handled.
>Does it mean the SCSI does not give a response for the block of data written.
>In otherwords does it mean that the response would be given after all the
>block of data is written for a single write request.
>
>Thanks
>Jay
>
>
>
>
>
>
>>===== Original Message From Mike Fedyk <mfedyk@matchmail.com> =====
>>On Wed, Dec 17, 2003 at 05:25:49PM -0500, Richard B. Johnson wrote:
>>
>>
>>>to the physical media. There are special file-systems (journaling)
>>>that guarantee that something, enough to recover the data, is
>>>written at periodic intervals.
>>>
>>>
>>Most journaling filesystems make guarantees on the filesystem meta-data, but
>>not on the data. Some like ext3, and reiserfs (with suse's journaling
>>patch) can journal the data, or order things so that the data is written
>>before any pointers (ie meta-data) make it to the disk so it will be harder
>>to loose data.
>>-
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Filesystems don't usually wait on the IO to complete before submitting
more IO in response to the next write() syscall. They can do this by
batching a whole bunch of operations into one committed transaction.

In reiser4 we do this more carefully than other filesystems such as
reiserfs v3, and as a result every fs operation is fully atomic.

--
Hans