[DRBD-user] meta-disk

[Clive Eisen]

Only if you told drbd to put the meta data on /boot

Not A Good Idea (tm).

Yes you mount the /dev/drbdx devices

If you are using linux-ha, you allow that to do the mounting.
--
Clive

Chip Burke wrote:

>Thank you very much for the very complete answer. I think I know what the
>issue is then. I have a separate /boot partition and it is only 100MB. The
>fact that it is only 100MB would not allow a 128MB file to be created. That
>makes sense. 
>
>My next question is, after read the linux-ha docs, it hints at this, but is
>not very explicit... In fstab am I to mount the new /dev/drbdx devices that
>are created instead of the normal /dev/hdx devices? 
>
>Thank you so much for your help,
>
>________________________________________
>Chip Burke
>________________________________________
>
>
>-----Original Message-----
>From: drbd-user-bounces at lists.linbit.com
>[mailto:drbd-user-bounces at lists.linbit.com] On Behalf Of Chris Procter
>Sent: Thursday, January 05, 2006 6:00 AM
>To: drbd-user at linbit.com
>Subject: Re: [DRBD-user] meta-disk
>
>On Wednesday 04 January 2006 20:07, Chip Burke wrote:
>
>  
>
>>I think I am missing something very basic. Do I need to create a partition
>>on the system specifically for the meta-data or something else? I have
>>    
>>
>read
>  
>
>>the drbd.conf notes about 10 times and I really don't understand what they
>>mean.
>>    
>>
>
>As with all good questions the answer is "it depends".
>
>DRBD needs to store 128MB of metadata some where on the system to store the 
>list of which blocks have changed (its stored on disk so it persists across 
>reboots). This metadata can be stored in one of two places.
>
>It can be stored on the partition you are replicating (termed "internal" 
>metadata) in which case it basically takes over the last 128MB of the 
>partition, reducing the space you have to store data in and overwriting and 
>data that is already stored there. This is good if you are starting fresh
>and 
>can overwrite the diskspace without risking the data or dont have room to 
>create a separate partition. 
>For this you put:
>meta-disk internal;
>in the drbd.conf for each machine (the "on [hostname]" section).
>
>Alternatively you can store the metadata on a separate partition ("external"
>
>metadata) in which case (obviously) you need to create a partition to use. 
>This partition needs to be at least 128MB for each DRBD device you are using
>
>and is setup in the drbd.conf file as: 
>meta-disk [devicename] [[offset]];
>e.g.
>meta-disk /dev/hde5 [0];
>
>The number in brackets is an offset within the partition, so the above will 
>use the first 128MB of the /dev/hde5 partion to store meta data, you could 
>then set up another drbd device (/dev/drbd1 say) with 
>meta-disk /dev/hde5 [1];
>which would use the second 128MB (obviously the partition would need to be
>at 
>least 256MB in size). You would then have the meta data for /dev/drbd0 in 
>0-127MB and for /dev/drbd1 in 128-256MB on /dev/hde5
>
>There are probably performance reasons for using one over the other, and
>there 
>are certainly issues with diskspace (if you dont have space to create a 
>seperate partion the internal is the way forward for example). In theory you
>
>could configure drbd to use internal metadata on one machine and external
>for 
>the same device on the other machine. If you do this however you're on your 
>own :-)
>
>Your error message implies that the meta-disk you are using is less then
>128MB 
>in size. I'm not sure if it defaults to something if you dont define it in 
>drbd.conf so its worth checking to make sure it is explicitly defined to 
>something sensible.
>
>Thats the way I understand it anyway, hope it helps.
>
>chris
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