Neil Perrin wrote:
>> I also noticed (perhaps by design) that a copy with compression off almost
>> instantly returns, but the writes continue LONG after the cp process claims
>> to be done. Is this normal?
>
> Yes this is normal. Unless the application is doing synchronous writes
> (eg DB) the file will be written to disk at the convenience of the FS.
> Most fs operate this way. It's too expensive to synchronously write
> out data, so it's batched up and written asynchronously.
>
>> Wouldn't closing the file ensure it was written to disk?
>
> No.
>
>> Is that tunable somewhere?
>
> No. For ZFS you can use sync(1M) which will force out all transactions
> for all files in the pool. That is expensive though.
>
> Neil.
Your application can call f[d]sync when it's done writing the file
and before it does the close if it wants all the data on disk.
This has been standard operating procedure for many, many
years.
From TFMP:
DESCRIPTION
The fsync() function moves all modified data and attributes
of the file descriptor fildes to a storage device. When
fsync() returns, all in-memory modified copies of buffers
associated with fildes have been written to the physical
medium. The fsync() function is different from sync(), which
schedules disk I/O for all files but returns before the I/O
completes. The fsync() function forces all outstanding data
operations to synchronized file integrity completion (see
fcntl.h(3HEAD) definition of O_SYNC.)
...
USAGE
The fsync() function should be used by applications that
require that a file be in a known state. For example, an
application that contains a simple transaction facility
might use fsync() to ensure that all changes to a file or
files caused by a given transaction were recorded on a
storage medium.
- Bart
--
Bart Smaalders Solaris Kernel Performance
[EMAIL PROTECTED] http://blogs.sun.com/barts
"You will contribute more with mercurial than with thunderbird."
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