Raw or cooked?
Wang Jean asked whether raw devices still beat cooked files for a 300GB Informix data warehouse on Solaris. Thomas J. Girsch said cooked files can be fast but are less reliable because OS caching may hide unwritten data, notably at checkpoints. David Williams said raw still wins. Paul Watson advised raw, as its code path is always shorter.
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We have a 300GB data warehouse in Informix with Raw device in Sun Solaris. Somebody suggested to use cooked files on faster disk drivers. I understand that Raw device has better performance and more reliable. Is it still the case? Are there any changes since Unix OS got lots of improvement now?
While it's true that sometimes cooked files can now be faster than raw devices, they are generally considered to be somewhat less reliable. This is because when you get that kind of speed out of cooked files, there's usually some kind of RAM caching going on. Which means that Informix will think that data has been written to disk when it really is still in RAM waiting to write. This is particularly important at checkpoint time. Some disk arrays also use cache, so you might experience this with raw slices as well, but in these cases the cache is hardware-based (not software-based) and is generally fault-tolerant. HTH, - Tom Girsch TJG Technical Services tgirsch@tjgtech.com Wang Jean <WANGJ@amtrak.com> wrote in message news:7uqluc$de7$1@news.xmission.com... > > We have a 300GB data warehouse in Informix with Raw device in Sun Solaris. > Somebody suggested to use cooked files on faster disk drivers. I understand > that Raw device has better performance and more reliable. Is it still the > case? Are there any changes since Unix OS got lots of improvement now? >
In article <7uqluc$de7$1@news.xmission.com>, Wang Jean <WANGJ@amtrak.com> writes > >We have a 300GB data warehouse in Informix with Raw device in Sun Solaris. >Somebody suggested to use cooked files on faster disk drivers. I understand >that Raw device has better performance and more reliable. Is it still the >case? Are there any changes since Unix OS got lots of improvement now? > Stil the case. -- David Williams
In article <7uqluc$de7$1@news.xmission.com>, WANGJ@amtrak.com (Wang Jean) wrote: > > We have a 300GB data warehouse in Informix with Raw device in Sun > Solaris. > Somebody suggested to use cooked files on faster disk drivers. I > understand > that Raw device has better performance and more reliable. Is it still > the > case? Are there any changes since Unix OS got lots of improvement now? > > Go for raw unless you have significant amounts of NVRAM in your RAID controller and all the raid is being down at a hardware level. Even then I'd still go for raw as I get my disk confirmations from the hardware NVRAM. So as far as the OS is concerned I've got drives with sub-millisecond response rates. If you compare like with like then raw is always without exception quicker, it has to be the code path to disk is significantly shorter. Paul Watson # I don't suffer from WF Software Ltd. # stress, I'm just Tel. (+44) 1436 674729 # a carrier Fax. (+44) 1436 678693 # www.wfsoftware.com