[DRBD-user] Drbd device limit, 8TB available from 16TB partition

Hari Sekhon hpsekhon at googlemail.com
Tue Dec 2 18:28:16 CET 2008

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


Lars Ellenberg wrote:
> On Tue, Dec 02, 2008 at 01:09:04PM +0000, Hari Sekhon wrote:
>   
>> Hi,
>>
>>   I have a server with just around 17TB usable storage which I want to  
>> replicate at the block level via drbd.
>>
>> I got the complaint regarding the 16TB max partition size supported, so  
>> reduced the 17TB partition to 16TB and successfully set up the drbd  
>> metadata on it.
>>
>> However, now I can only see 8TB of it.
>> I understand the limit is 8TB having looking through previous mails to  
>> the this list, but then why did it let me use up a 16TB partition and  
>> waste half of it?
>>     
>
> drbd used to be able to handle 4 TB at max.
> then some drbd can handle 8 TB on 64bit kernels,
> but incorrectly pretended it could support 16 TB.
>
> that was then fixed in more recent drbd, to actually only support 8TB,
> and don't try to use more, as otherwise you'd Oops the kernel sooner or later.
>
> and now, even more recent drbd, namely drbd 8.3 (to be released "soon"),
> supports 16 TB (even on 32bit kernel!).  it will then probably support
> even more (probably only on 64bit kernel, though) with some of its
> dot-releases.
>
>   
>> This is running on a x86_64 CentOS 5 server with drbd 0.8.13 (I had been  
>> using drbd 2.8 but this kept crashing the system with a kernel panic  
>> when trying to write to the mounted drbd0 partition with xfs on it.  
>> Downgrading to 8.0.13 and then re-creating the metadata, mounting and  
>> retrying solved the problem)
>>
>> Is there any way of getting the thing to do all 16TB of the partition?
>>
>> Otherwise I'll have to destroy it and rework it with 2x8TB which would  
>> be a pain. I'd then be tempted to do an lvm on the top of those 2 drbds  
>> even though I know Lars recommends against it, because I really could do  
>> with the 16TB contiguous space replicated...
>>     
>
> try drbd 8.3, even though its a release candidate only, right now.
>   
Ok I fetched 8.3 to try it out, but now I've got an error building. I'll 
post it separately though. to not hijack my own thread...

-h

-- 
Hari Sekhon
Always open to interesting opportunities
http://www.linkedin.com/in/harisekhon




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