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raw and block device files

himacs
Super Advisor

raw and block device files

Hi,


1.I just want to know the difference between block and raw device files.As per my knowledge block files are used to store datas in hard disk.Then whats the role of raw files.I have heard that raw device used to store dbf files.
I think raw devices are logical,will be used while initializing the hard disk.

2. How we can create a vg for raw files only.

Please help me to understand this

Regards,
himacs
3 REPLIES
Robert-Jan Goossens
Honored Contributor

Re: raw and block device files

Hi,

Have a look at this thread.

http://forums11.itrc.hp.com/service/forums/questionanswer.do?threadId=987277

2. How we can create a vg for raw files only.

create a volume group, create a logical volume without creating the filesystem, change the permissions of the raw logical volume device names to the application owner.

Regards,
Robert-Jan
Venkatesh BL
Honored Contributor

Re: raw and block device files

Johnson Punniyalingam
Honored Contributor

Re: raw and block device files

Raw devices bypass the buffer cache and use DMA directly to/from the program's I/O buffers; they are normally restricted to full-sector transfers. Using raw devices generally will give you faster performance. Raw devices are used when making new filesystems, when checking unmounted filesystems, or for copying quiescent filesystems. The block devices are used to mount filesystems. Each disk has a block device interface where the system makes the device byte addressable and you can write a single byte in the middle of the disk.

>>2. How we can create a vg for raw files only.<<
Example:-
How to creat raw device !
/usr/sbin/lvcreate -L 500 -n syb_trans_data8 vg_raw

vgname : vg_raw
(do'not create new file system) meaning

step1:- lvcreate -L
step2:- chown oracle:dba /dev/vgxx/rlvolxx

stop. (we have done) please pass on the infor of the raw device file to DBA or App's Team

Thx,
Johnson

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