Re: Oracle 9i Linux and raw devices

From: Peter J. Holzer <hjp-usenet_at_hjp.at>
Date: Sun, 13 Apr 2003 21:42:09 +0200
Message-ID: <slrnb9jfch.sgj.hjp-usenet@teal.hjp.at>

On 2003-04-13 02:16, Andreas <ast1200_at_netscape.net> wrote:
> sorry, I didn't wrote it clear. THE MAX OF 256 RAW devices it's LINUX
> KERNEL LIMIT (the major num. for raw dev is only 8 bit), NOT ORACLE LIMIT.

That's not true. While the minor number (the major number selects the driver and is irrelevant in for the number of disk devices) is limited to 255, the real number of devices depends on the kind of device you are using:

For SCSI disks, you can have up to 15 partitions per disk, and the number of disks is configurable at compile time (56 on a stock Redhat 7.3 system - so that would give you up to 840 raw devices).

For MD and LVM devices, I think the limit is indeed 256 each.

There is of course also devfs, which may lift some of these limits.

> > Basically, lseek and ftell (the OS routines for postioning within
> > files) accept 64 bit arguments on 64-bit environments and 32 bit
> > arguments on 32-bit systems. The 1st bit is the sign and signfies
> > the direction of the movement (fwd/bckwd). The 32bit routines can be
> > used to move within 2GB files, not larger. Unless you have things
> > like ftell64 or lseek64 (64 bit env.), you are stuck with the 2GB
> > limit.
>
> Yes, it's correct if create data files on a FORMATED FILES SYSTEM,
> but it work different on RAW DEVICE,

Actually it's almost the same. It's just that on Linux supported ftell64 and lseek64 for a long time on block devices, while the support in the VFS layer was broken until the 2.4 kernel.

> the raw device isn't formated
> by the OS and each RAW device is a single data file.

                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

>
> It'a a fragment of Oracle documentation:
> "Oracle9iR2 on Linux: Performance,Reliability and Manageability
> Enhancements on Red Hat LinuxAdvanced Server 2.1"
>
> ...
> 64-bit File I/O
> Linux supports 64-bit file I/O even on 32-bit platforms like Intel
> Pentiumbased
> servers. Oracle9iR2 supports 64-bit file offsets internally, hence there
> are no 2GB or 4GB limitations on data, log and control files. The limits
> on number of files per database (64K), number of blocks per file (4
> million), and
> maximum block size (16KB) are common to other Oracle platforms. Based on
> these limits, the maximum size for a database file is 64GB, and the maximum

                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

I think you just answered your own question.

> database size with 16KB blocks is 4 petabytes.
> ...
>
> is the raw device limit 4 PB?

I don't think so.

-- 
   _  | Peter J. Holzer    | Latein ist das humanoide Äquivalent
|_|_) | Sysadmin WSR       | zu Fortran.
| |   | hjp_at_hjp.at         |
__/   | http://www.hjp.at/ |    -- Alexander Bartolich in at.linux

Received on Sun Apr 13 2003 - 14:42:09 CDT