[DRBD-user] drbd-user Digest, Vol 119, Issue 22

Bret Mette bret.mette at dbihosting.com
Thu Jun 26 20:15:08 CEST 2014

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


If you replace the disk DRBD would also need to resync everything. Why would you want a secondary disk with some arbitrary set if incremental data backups? It's only useful if you have a full sync.

I find DRBD to be less tolerant to data inconsistency and is much more likely to perform a resync than md.

- Bret

> On Jun 26, 2014, at 6:12 AM, Allen Chen <achen at harbourfrontcentre.com> wrote:
>> On 6/26/2014 6:00 AM, drbd-user-request at lists.linbit.com wrote:
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>> Today's Topics:
>>    1. Re: Sync to the same IP (Lars Ellenberg)
>> ----------------------------------------------------------------------
>> Message: 1
>> Date: Thu, 26 Jun 2014 11:11:23 +0200
>> From: Lars Ellenberg <lars.ellenberg at linbit.com>
>> Subject: Re: [DRBD-user] Sync to the same IP
>> To: drbd-user at lists.linbit.com
>> Message-ID: <20140626091123.GH17123 at soda.linbit>
>> Content-Type: text/plain; charset=us-ascii
>>> On Thu, Jun 19, 2014 at 01:23:56AM +0200, Alexey Orishko wrote:
>>> Hi all,
>>> I got recently across DRBD and it looks like a cool stuff.
>>> I wonder if someone could clarify for me if it is possible to
>>> configure DRBD to sync one block device to another block device on the
>>> same host?
>> yes you can
>>    (example of how to do that was provided in the thread already;
>>     yes you can use; no you don't need ip aliases)
>> No, I don't think that's a good idea.
>>> On Sun, Jun 22, 2014 at 10:56:21PM +0200, Alexey Orishko wrote:
>>>> On Sun, Jun 22, 2014 at 7:38 PM, Bret Mette <bret.mette at dbihosting.com> wrote:
>>>> I would still like to know what the purpose is for this. You're picking the
>>>> brains of the community for a solution to your problem, it would be nice to
>>>> give a little back and share the backstory about that problem.
>>> I want to figure out if DRBD is suitable for making a second copy of
>>> backup disk without stopping client.
>> Explain to me why md raid1 won't do what you want.
>> Same question to the
>> "Someone talked about this on some Amazon event,
>> and I want to do what he thinks is cool" fraction.
>> This is host based mirroring.
>> md raid1 is meant to do that.
>> Why not use it?
>> Oh, so you want it async...
>> Did you know about mdadm "write-mostly" and "write-behind"?
>> It's not that DRBD cannot do it.
>> It's just that I think it is the wrong tool for the job.
>> So please explain to me why you think otherwise.
>>    Lars
> Hi Lars,
> Here is my explanation to use DRBD instead of md raid1:
> for md raid1, if one member is physically removed from the machine, and after you reconnect the same disk to md raid1, MD will re-sync everything to it. It takes much more time.
> for DRBD, if the second disk is removed from the machine, and after you reconnect the same disk to DRBD, DRBD will sync whatever has been changed. It take less time than MD raid1.
> So I need someone to confirm DRBD will work with primary and second nodes on the same machine.
> Thanks,
> Allen
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