Re: [Ext2-devel] [RFC 0/13] extents and 48bit ext3

Laurent Vivier
2006-06-20T09:21:19Z

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Jeff Garzik wrote:
> Laurent Vivier wrote:
>> Qi Yong wrote:
>>> Linus Torvalds wrote:
>>>
>>>> On Fri, 9 Jun 2006, Stephen C. Tweedie wrote:
>>>>
>>>>
>>>>> When is the Linux syscall interface enough? When should we just
>>>>> bump it
>>>>> and cut out all the compatibility interfaces?
>>>>>
>>>>> No, we don't; we let people configure certain obsolete bits out (a.out
>>>>> support etc), but we keep it in the tree despite the indirection
>>>>> cost to
>>>>> maintain multiple interfaces etc.
>>>>>
>>>> Right. WE ADD NEW SYSTEM CALLS. WE DO NOT EXTEND THE OLD ONES IN
>>>> WAYS THAT MIGHT BREAK OLD USERS.
>>>>
>>>> Your point was exactly what?
>>>>
>>>> Btw, where did that 2TB limit number come from? Afaik, it should be
>>>> 16TB for a 4kB filesystem, no?
>>>>
>>>>
>>> Partition tables describe partitions in units of one sector.
>>> 2^(32+9) = 2T
>>>
>>> To prevent integer overflow, we should use only 31 bits of a 32-bit
>>> integer.
>>> 2^(31+12) = 8T
>>>
>>> There's _terrible_ hacks to really get to 16T.
>>>
>>> -- qiyong
>>>
>>
>> IMHO, a simple solution is to use "Logical Volume Manager" instead of
>> partition
>> manager: we create 64bit filesystem in a Logical Volume, not in a
>> partition.
>
> That doesn't solve anything, if you are not using a 64bit filesystem.

Sorry, I don't undestand why ???

You can use 32bit filesystem too, but you limit the size of the logical volume
to be compatible with the filesystem you use. LVM allows to create several 32bit
volumes on a big (> 8T) disk (if exists)

But if we think further, as biggest disk is 750 GB (and I think even using HW
RAID, there is an HW limit something like 4 TB), we can imagine a big Volume
Group belonging several Physical Volumes divided in Logical Volumes: so we
already use LVM, we don't need partition...)

>> "partitioning is obsolete" ;-)
>
> LVM is nothing but a partition manager...

LVM is more than a partition manager:
- it is arch-independent
- it is 64bit compliant
- it can gather together several disks
- it is flexible (you can add/remove/resize volume)
- it is modern (doesn't have primary/extended partition, doesn't have limited
number of partition)

so... it's a volume manager.

Regards,
Laurent
--
Laurent Vivier
Bull, Architect of an Open World (TM)
http://www.bullopensource.org/ext4

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