[DRBD-user] device size limit <= 2TB for DRBD disk on DRBD <= 0.7.3

Philipp Reisner philipp.reisner at linbit.com
Wed Sep 1 13:21:25 CEST 2004

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.

On Wednesday 01 September 2004 01:27, Helmut Wollmersdorfer wrote:
> Lars Ellenberg wrote:
> > two drbd with ca. 2TB each will do, probably.  three is unlikely, and
> > four of that size is probably not possible currently.
> >
> > this is a known problem, and will eventually be fixed.
> > it does not seem very hard to fix, but as long as we have the impression
> > that "the average drbd user" does not use several TB of storage, fixing
> > that has low priority...
> Hmm, times are changing very fast. Two years ago I had 12 GB on servers
> and 50 GB in total at home office. Now I have 2 x 240 GB on servers and
> around 1 TB in total.
> At last project they had 27 TB storage system on one server (for _one_
> application) and 17 TB of this mirrored by 11 km fiber to an hot standby
> - not DRBD, obviously.

There are several Limits involved:

1. The 32bit overrun in DRBD's size determination code.
2. The limit in the kernel's vm - space. Limiting the memory for the bitmaps.
3. Current meta-data layout allows 3.8TB per device.

(1) will be fixed rather soon. 

(2) applies only to i386, this is not an issue on an 64 bit architecture
    If LINBIT's customers demand a fix for this problem, we will fix it
    for i386 -> I.e. if you want to have that limit removed, ask LINBIT!

(3) Will be on drbd-8's roadmap.

: Dipl-Ing Philipp Reisner                      Tel +43-1-8178292-50 :
: LINBIT Information Technologies GmbH          Fax +43-1-8178292-82 :
: Schönbrunnerstr 244, 1120 Vienna, Austria    http://www.linbit.com :

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