Re: raw device on RedHat Linux

On Wednesday 22 November 2000 00:00, you wrote: > Does anyone know whether RedHat Linux 7.0 supports raw device? I got 6.2 > installed at home but it doesn't support raw device. I believe raw device > is much better for informix performance. > Hello, what do you mean, it doesn't support raw device ? There is nothing to support. I installed informix on SuSE6.2 and put data onto raw device. I just left a disk partition blank and unmounted. That was partition /dev/hdb1. Since I just installed informix to test it, I put the data into rootdbs. The path for rootdbs was /dev/hdb1 and that's it. Informix can write to it, without OS knowing about it. lp, Mitja Zabukovec

In article <8vfvad$spb$1@news.xmission.com>, Mitja Zabukovec <mitja.zabukovec@mais.si> wrote: > >On Wednesday 22 November 2000 00:00, you wrote: >> Does anyone know whether RedHat Linux 7.0 supports raw device? I got 6.2 >> installed at home but it doesn't support raw device. I believe raw device >> is much better for informix performance. >> > >what do you mean, it doesn't support raw device ? >There is nothing to support. >I installed informix on SuSE6.2 and put data onto raw device. >I just left a disk partition blank and unmounted. That was partition >/dev/hdb1. Since I just installed informix to test it, I put the data into >rootdbs. The path for rootdbs was /dev/hdb1 and that's it. >Informix can write to it, without OS knowing about it. That's not a raw device. That's still the block device for which accesses will go via page/buffer cache. A *raw* devices is a character device interface for which reads/writes go directly and synchronously to the underlying disk. RedHat 7.0 include the raw device kernel patch in their distribution and provide access to that via the userland utility raw(1) and via the config file /etc/sysconfig/rawdevices which sets up your raw bindings automatically at boot time. The file initially contains the following comments as explanation: # raw device bindings # format: <rawdev> <major> <minor> # <rawdev> <blockdev> # example: /dev/raw/raw1 /dev/sda1 # /dev/raw/raw2 8 5 As it says, add lines to this file of the form /dev/raw/raw1 /dev/sda1 /dev/raw/raw2 /dev/sda2 ... and then /etc/rc.d/init.d/rawdevices restart which do the necessary commands to set up the bindings (and that will automatically be run at each boot time too). You can then tell your raw-device-using software (Informix here) to use the devices /dev/raw/raw1, ... as raw devices. You probably ought to check with Informix (or others on this newsgroup who may know) that Informix is OK to use with raw devices on Linux: for example, the raw device interface only allows reads/writes of 512-byte multiples which are 512-byte aligned. It's possible (though I'd guess unlikely) that Informix needs the raw device to be more lenient about what reads and writes it allows or that it expects some other additional interface (ioctls say) in addition to the mere existence of the device. --Malcolm -- Malcolm Beattie <mbeattie@sable.ox.ac.uk> Oxford University Computing Services "I permitted that as a demonstration of futility" --Grey Roger