PFS from INODZ

This is how i'm gonna implement pools......

* Every disk that is present in the system is controlled by a driver.
* every driver has a request queue.

I will create a virtual device - POOL. Pool's size = sum of sizes all the devices tat forms the pool.
any request that comes to my Pool's request queue will be forwarded to a corresponding physical device
-------------------------
| DEV-A | DEV-B | DEV-C | > dev_name
| 0-100 | 0-100 | 0-100 | > size in sectors
-------------------------
........................||...........................
........................||...........................
.......................\_/........................
........................\/.........................
---------------------------
| .........POOL ..........|
| ......... 300 ..........|
---------------------------


so, this pool is only visible to the user.
Any I/O request to the POOL should be converted to I/O request of the device.
Example : any request to read the 125'th sector of the pool, should be a request to read the DEV-B's 25th sector.

please see,
http://lwn.net/Articles/58720/

In this device driver,
static void sbd_transfer(); does the copying job from buffer to disk....

I need to modify this sbd_transfer(), such that,
{
if(sector>= 0 && sector <100)  class="Apple-tab-span" style="white-space:pre"> i/o request should be sent to DEV-A's driver...


if(sector>= 100 && sector <200) class="Apple-tab-span" style="white-space:pre"> i/o request should be sent to DEV-B's driver...


if(sector>= 200 && sector <300) class="Apple-tab-span" style="white-space:pre"> i/o request should be sent to DEV-C's driver...

}
This is the algorithm

Questions.
* Is this possible ?
* If this is possible, how can we enable communication between Drivers?
[pool's driver need to pass a read/write request to DEV-B.. HOW?]

PFS will have 2 main modules.....
1. Pool manager
2. File system.

* Pool manager is the one tat should replace the volume manager.
The Pool Manager should handle multiple disks as a single logical pool. the size of that logical pool should not be limited. the size should grow when another disk is added to the pool, it should decreased when a disk is removed.! It should provide various functions to the file system tat will be sitting above this.

* the File System - PFS is the one tat interacts with the Pool Manager to get the data written into the hard disk. For this, the FS makes use of the methods provided by the pool manager. This interacts with the upper level layers like system calls etc.

Here is a detailed Description of the PFS...

Current filesystems have this problem : LIMITED SIZE...
u allocate certain size for a file system, format a file system, done.!

say,
in a 50 hard disk, u have 3 logical partitions
MOVIES | PROJECTS | DOCUMENTS..
20GB........20GB...........10GB

* now consider MOVIES partion is full
* there is 15GB free space in PROJECTS
* still u cant add even a single file in MOVIES !!!

Why not make a file system tat can dynamically expand and shrink...
We'll eliminate the term "VOLUMES, PARTITIONS"... We'll make POOLS!!!

Now, how about,
* MOVIES , PROJECTS, DOCUMENTS share the same 50GB.
* there is no seperate size for each of these.
* data can be added into any of these, till the whole 50GB gets full...
* still MOVIES , PROJECTS, DOCUMENTS can be accesed as different file systems
* they can be mounted, and un mounted seperately..

Now,
* u buy a new harddisk (120 GB)
* u plug-in the harddisk...
* boot ur system...
* "a single command" (pool -add /dev/my_new_harddisk already_existing_pool)
* NO-RE-FORMATTING ur harddisk
* [new space 50 + 120 GB]
* data can be added into any of MOVIES , PROJECTS, DOCUMENTS , till the whole 50GB + 120GB gets full...

it is already implemented in,
ZFS......... Open solaris
ZFS-on-FUSE. LINUX
LVM2 can do this (but not as a readymade file system)