[DRBD-user] Dual Primary Mode: Shared Directory blocked after node crash until reboot

DRBD User DRBDUser at gmx.at
Tue May 12 13:09:31 CEST 2015

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


Hi

@Cesar: thx for your suggestion - but i don't want to do a manually fence.

during testing i found out, that after pulling power plug the shared directory it is not completely inaccessible : it is readable, only a write will block until crashed node restarts - BUT what if crashed node never restarts ? (my service saves it state into shared directory an should not block)

maybe its better to switch from active/active to active/passive - or is here the situation (pull power plug, blocking..) the same ?
 
thx

Gesendet: Dienstag, 12. Mai 2015 um 12:33 Uhr
Von: "Cesar Peschiera" <brain at click.com.py>
An: "DRBD User" <DRBDUser at gmx.at>, drbd-user at lists.linbit.com
Betreff: Re: [DRBD-user] Dual Primary Mode: Shared Directory blocked after node crash until reboot

About of your problem of fence:
 
Instead of use a fence by Hardware, you can use a manual fence that come with the cluster software.
 
Please read this:
1- It not require any hardware.
2- This option isn't advisable in production environments, but useful in development environments.
3- The file used is "fence_ack_manual"
4- It is executed by CLI in a node that is alive for apply the fence to other server.
5- For use it, It is advisable that first disconnect totally the electric power on the server that will be fenced, the goal is to shut down brutally the server that will be fenced before of run the fence command.
6- Finally, execute this command in a node that is alive:
Shell# /[PATH]/fence_ack_manual [IP or Name of the Node that will be fenced]
7- Follow the steps as directed by this command.
 
I hope this information is helpful.
 
Best regards
Cesar
 
----- Original Message -----
From: DRBD User[DRBDUser at gmx.at]
To: drbd-user at lists.linbit.com[drbd-user at lists.linbit.com]
Sent: Tuesday, May 12, 2015 5:39 AM
Subject: [DRBD-user] Dual Primary Mode: Shared Directory blocked after node crash until reboot
 

the DRBD status is (regardless of 'nice' shutdown (eg reboot) or 'abrupt' kill (eg pull power plug))
 
cs:WFConnection ro:Primary/Unknown ds:UpToDate/Outdated
 
but only with a 'nice' shutdown the shared directoy is still accessible...
 

Gesendet: Dienstag, 12. Mai 2015 um 09:44 Uhr
Von: Digimer <lists at alteeve.ca[lists at alteeve.ca]>
An: "DRBD User" <DRBDUser at gmx.at>, drbd-user at lists.linbit.com
Betreff: Re: [DRBD-user] Dual Primary Mode: Shared Directory blocked after node crash until reboot
On 12/05/15 03:42 AM, DRBD User wrote:
>>>> pacemakers pcs property stonith-enabled is currently set to false
>
>> Well there's your problem. :)
>
> Since i don't have any (hardware) STONITH device, i have set stonith-enabled to false.
> DRBD's fencing rule is set to : 'fencing: resource-only'
>
> My goal is: if one node crashes, the other node should take over the work immediately. But actually i have to wait the reboot time of the crashed node. I thought, that in such a situation the active node (rather the shared directory) is immediately usable ?
>
> May be i should use another fence script ?
>
> I tried to create the resource with operation 'on-fail=restart' - but no success ...
>
> Any other suggestions ?

You *CAN NOT* safely proceed when a node stops responding _until_ you
have put the lost node into a known state. To do otherwise would be to
risk a split-brain.

A good fence device are switched PDUs, like the APC-brand AP7900 (not
all makes/models are supported, so check first before buying other
brands). The AP7900 can usually be found used for ~$200 and makes an
excellent external fence device.

Trying to use DRBD without proper fencing will result in pain and
heartache. The delay needed to fence a lost node is FAR preferable to
risking a split-brain.

--
Digimer
Papers and Projects: https://alteeve.ca/w/[https://alteeve.ca/w/]
What if the cure for cancer is trapped in the mind of a person without
access to education?
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