Re: Files or RAW-Devices ?

Wachs Rene <Rene.Wachs_at_ezv.admin.ch> wrote:

>This summer our DEC Alpha 4000 will be replaced by a DEC 8xxxx. Today we have a 20
>GB-DB with mainly 2 large-tabs (6.5 GB-Tab with 12 mio. rows, 3.5 GB-Tab with 7
>mio. rows). Performance is satisfactory, but sometimes multiuser behaviour is
>really bad. Nobody can explain that - neither Digital nor Oracle.
 

>DEC says : on the new DEC-Box don't make Files ! Make raw-Devices ! This will
>increase performance and improve the multiuser behaviour.

I've found that raw devices are a pain to admin and the performance increases vary from machine to machine. We are converting from a DEC VAX 7310 to a DEC Alpha 8200 (70Gb database). If you are having problems with a multi-user environment, the first things I would look for would be how you are doing REDO's. I tend to use lots of smaller ones to keep the checkpoint/archive processes from being a large spike in the system.

If you are going through a cluster controller, you should check to see if your star-coupler is saturated. Ours is capable of moving 8Mb/sec, and was moving 6.5Mb/sec continuously. We have three VAXes, about 120Gb disk space and 2 DLT tape drives attached. I've doubled our throughput for about 10k with another star coupler.

Going through the cluster, it doesn't make a lot of difference whether we use raw or file system based tablespace files. Now, on the other hand, our Sun SparcServer 2000e runs rather nicely under raw. Our data warehouse (werehouse? ;-) ) runs PQO and has a lot more I/O throughput available. The difference was more on the order of a 10-15% difference.

The data warehouse is still under development, so I don't know if I'll keep the raw partitions due to backup and management considerations, but the Sun GUI makes it a lot easier to fool around with the Sun storage arrays.

                                Hope this helps.

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