Unanswered: ASE 12.0 raw partition/regular filesystem
We are currently running ASE 12.0 on a Sun E3000 server with the database on raw partitions. As we are moving to new hardware soon I was wondering if we still need raw partitions or if we might as well use regular file systems.
Response time for read operations is generally better for devices
stored on UNIX operating system files as compared to devices
stored on raw partitions. Data from device files can benefit from
the UNIX file system cache as well as the Adaptive Server cache,
and more reads may take place without requiring physical disk
The raw partion is more secured than the file systems. theirfore you can use raw partion for yr production server and file systems for developement server.
We use Unix file systems on all our post 12.0 Production servers,
we have not experienced performance issues. It gives a great
deal more flexibility in terms of moving or copying server to other machines and removes reliance on Unix sa's to administer raw devices.
Make sure you turn dsync off for production systems to ensure data
integrity, which means writes will suffer but reads are still buffered.
However this is a big topic with a lot of arguments on both sides. I have heard best performance is achieved if you have Veritas file systems, but this costs.
Thanks the both of you for your reply. It's very usefull to me.
Performance won't be that much of an issue since we are moving to a MUCH faster system... I'm only looking at ease of administration (backup and recovery!) .
One of the thing with the combination Sybase flat file I hear people talking about is the caching of Sybase not working properly together with OS caching resulting in database corruption in case of a system crash. Is this solved by turning dsync off?
Ben, that is correct. DSYNC will avoid the write-cache (which could lead to the OS telling ASE something was written and then a crash which would wipe out the cache'd data) and provide better data integrity. Note you lose performance since writing to a buffer is of course much faster than requiring synch'ed data.
We were on 11.9.2 for Linux for around 6 months with OS files (11.9.2 did not have the dsync flag so all were buffered) and encountered no data loss. We have since moved to 12.5 for linux and turned Dsync ON 'just in case' and did notice a performance hit.
From what I understand, at least in Linux, filesystem files do not support async I/O which raw devices do. The next Linux patch (126.96.36.199) is slated to have Async I/O capability on the 2.4 kernels. I think once that is out, there will be no advantage to having RAW vs. File System + Dsync.