Re: [Drbd-dev] larger than 4tb volume status

[Philipp Reisner <philipp.reisner@linbit.com>]

Am Donnerstag, 16. November 2006 10:06 schrieben Sie:
> >  * Selling DRBD+ licenses
>
> The web site doesn't make clear what is DRBD's current limitation, it
> states
>
>
> - "single device is limited to 4 TB"
> - "DRBD+ uses HIGHMEM[...]necessary in order to mirror over 4 TB in total
> over all devices"
>
>
> So, is it 4 TB total storage per node or 4 TB per drbd volume ? Is this
> different for 32 bits and 64 bits systems ?
>
>

I hope you do not use a proportional font to read your email:

              |         DRBD        |          DRBD+
--------------+---------------------+------------------------
per Device    |    4TiB             |    16iBT on 32bit  (2)
total         | ~4TiB on 32 bit (1) |    unlimited       (3)


(2) on 64 bit it is 2^72 Byte or 4 ZiByte or 4294967296 TiB

(1) You can do tricks with the kernel parameter vmalloc= 
    I do not know the exact limit by heart, but I guess you
    will not be able to reach 6 TB on a 32 bit system.
    On a 64 bit system it might be more (with vmalloc= tricks),
    but I do not know.

(3) Unlimited. But limited by available system RAM. DRBD 
    allocates 32KiByte BitMap (in RAM) for 1GiByte of Storage.

    Storage size   |  DRBD's RAM usage
    ---------------+------------------
       1 TiB       |       32 MiB
       32 TiB      |       1 GiB
       ...                 ...

PS: The largest Volume I know of running in production is 20TB!

-Phil
-- 
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