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    SubjectRe: blocks or KB? (was: .. current meaning of blk_size array)
    On Nov 14, 2001  21:41 +0100, Peter T. Breuer wrote:
    > "A month of sundays ago Martin Dalecki wrote:"
    > > "Peter T. Breuer" wrote:
    > > > Is blk_size[][] supposed to contain the size in KB or blocks?
    > > There is no rumor it's in blocks.
    > Maybe I misinterpret what you write. I interpret it as meaning "the
    > rumour is not a rumour but a fact. It is in blocks".

    Check what /proc/partitions shows us. #blocks, with units of 1kB.
    This has been standard in the kernel for a loooong time.

    > The point is that if blk_size counts in KB, then the size of a device
    > cannot reach more that 2^32 * 2^10 = 2^42 = 4TB. I'd personally say
    > 2TB, becuase the int blk_size number is signed.
    > That's rumoured not to be the case, and the max size of a device is
    > supposed to be about 8 to 16TB. Let's suppose the rumour is true ..

    Well, the rumor is wrong. There has always been a single-device 1TB/2TB
    limit in the kernel (2^31 or 2^32 * 512 byte sector size), and until
    recently it has not been a problem. To remove the problem Jens Axboe
    (I think, or Ben LaHaise, can't remember) has a patch to support 64-bit
    block counts and has been tested with > 2TB devices.

    > So we deduce that one has to assign a different meaning for the blk_size
    > array. "count in blocks" is how the rumour goes. That way you can get
    > 4 times higher sizes .. all the way to 8 or 16TB per device. And this
    > is what is rumoured to be the case.

    Where do you get these rumors?

    > It should be in blocks if the size of a device is to reach 8 or 16TB.
    > If it is in KB, we are limited to 2 or 4TB.

    In theory this is possible (it was discussed on the LVM list a bit), but
    it would take a bunch of work to make it real. For LVM (and MD RAID),
    since we are dealing with multiple real devices < 2TB in size, we could
    use a blocksize of 4kB to get a larger virtual device. In the end this
    only wins for a short time and you need 64-bit block numbers anyways.

    > Persuade me that this is not a bug, and an important one at that :-)
    > Hellloooooo everybody! Linux cannot manage partitions greater than
    > 4TB, ha ha ha hhhhhaaaa! ;-)

    And it can't handle more than 64GB of RAM on ia32 (was previously 1GB).
    So what? When a limit is reached for any reasonable number of people,
    it is fixed.

    > I at least am getting up to devicesizes at the 8TB range.

    If you are in that ballpark, then get the 64-bit blocknumber patch, and
    start testing/fixing, instead of complaining.

    Cheers, Andreas
    Andreas Dilger

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