Re: 2Gb Exp problems 8.1.7

Frank wrote:

> Could some OS guru elaborate on why some OS's only handle 2GB?
> Seems to me these must be 31 bit then. (AIX 4.x had a special
> 'add-on' to go beyond 2GB, looked like the MSB was enabled, so to speak)

Won't call myself an OS guru, but I will have a bash (don't like ksh or csh that much ;-).

Firstly, it has _nothing_ to do with operating system and _everything_ to do with the file system.

And this type of problem has been around for a long while. Back in my mainframe days, the filesystem used on the Siemens BS2000 o/s (still IMO one of the best mainframe o/s's ever) used a single byte for storing extent number. Thus you were limited to 255 extents. (wasn't this also the case with Oracle extents a few versions ago?)

Using DOS old FAT16 filesystem is no different. The File Allocation Table has also size restrictions. Thus, a completed path of a subdirectory can only be (if I recall correctly) also 255-256 characters in total. When you reached that limit, you can not create any more subdirectories.

Okay, now for ionodes and Unix. A file is represented by a structure called an inode (similar to a FAT entry).

Each inode contains stuff like file type, access rights, timestamps, size, pointers to data blocks, and so on. A bunch of data blocks make up a file. Their addresses are stored in that file's inode.

An ionode is of a certain size. Thus, you are limited to the number of data block pointers (or addresses) you can store in the ionode of a file.

Here are a table listing Unix filesystems used by Linux through the years:

                      Minix ext ext2
Max fileystem size    64MB  2GB 4TB
Max file size         64MB  2GB 2GB 

Because operating systems are closely tied to specific filesystems (often only running on a single specific filesystem), filesystem limitation such as the 2GB filesize limit is seen as an operating system issue. Which is not really the case as that limitation belongs solely to the filesystem.

--
Billy