fs/raw device

[Gerald_13]

hi,
I would like to know what's mean a fs in mode raw device.
In a VG (example : /dev/vg00) , why there are some lv in raw device and caracter device (exemple : rlv00 associate with lv00). what's mean?
thank's very much for your help and sorry for my bad english.
regards,
Gerald

[Stefan Farrelly]

Each lvol created has a raw (character) device file AND a block device file, eg;
/dev/vg00/lvol1 and /dev/vg00/rlvol1.

Normally the block device is used, and each lvol is mounted (so you can see it in bdf). But you dont need to use it this way. An application like a database can read/write direct to the raw (character) device without that lvol being mounted. This is faster as it bypassess the unix kernel buffercache, thats why some applications use them.

[MANOJ SRIVASTAVA]

Hi Gerald


The differnce is that the both point to same area , however opne is a Blcok Special file adn the other is a character special file . incase you are adressing the fiels system as a block special on e ( like in for eg in dd or in oracle using raw fiels sytems , or even fsck ) you would use the raw device , however if you are wirintg or mounting ona direcotry then you would need is a character device or the formatted filesystem.


Manoj Srivastava

[Jose Mosquera]

Hi,

For general norm this is observed with more frequency to the moment to create database areas, for this case the most palpable difference is that your will never be able to make a copy of security of a raw area directly because the format of the information stored in this area depends on a third part software, in this case you need do export database data to any standard (cooked) fs through the any export utility. However from a non-raw area (colloquially **cooked**) it can support managed files and interpreted directly by the operating system.

I believe that your question is born of something related with databases, I wait to have clarified you something with this simple example.

Rgds.