Raw vs. Cooked files
A user installing IDS 10 on Red Hat Enterprise Linux 3 (x86) asked whether to use raw devices or cooked files for dbspaces. He quoted an old FAQ entry (Art Kagel, 1998) showing raw disk benchmarks clearly faster than cooked/filesystem files because writes bypass the UNIX buffer cache, and asked whether that still held given improvements in filesystems had supposedly narrowed the gap. The thread contains only this one posting; no replies or resolution are recorded.
Auto-generated by DrWatson from the posts below — may be imperfect; read the full thread.
Hello, I am installing IDS 10 on RHEL3 on an intel x86 server. I need to make the choice between raw devices and cooked files. I found the following information in the FAQ's. Is this information still accurate? Do cooked files continue to be significantly slower than the raw files? I have heard that UNIX file systems have improved over the years and the performance divide between raw and cooked files has narrowed considerabley. Is it true? Thanks! - Rajesh -------------------------------------------------------------------------------------- 6.38 Is raw disk faster than cooked files? On 22nd Jun 1998 kagel@bloomberg.net (Art S. Kagel) wrote:- ....................the safety issue of cooked files is no longer a problem. The big problem with cooked files still is performance. All writes and reads to/from cooked files MUST go through the UNIX buffer cache. This means an additional copy from the server's output buffer to the UNIX buffer page then a synchronous write to disk. This is opposed to a write to a way file where the server's output buffer is written directly to disk without the intervening copy. This is just faster. Anyone who has written anything that can test this can attest to the difference in speed. Here are my test results: FileType Sync? Times (real/user/system) 2run avg --------------- ----- ----------------------------------------- Filesystem file N 14.40/3.70/2.52 Y 15.02/3.61/2.63 Cooked disk N 12.81/3.74/2.24 Y 13.42/3.84/2.43 Raw disk N 9.32/3.67/1.52 Y 9.40/3.66/1.44