[DRBD-user] drbd implementation question

[Rudi Ahlers]

----- Message from rwalker at medallion.com ---------
    Date: Fri, 19 Oct 2007 09:53:20 -0400
    From: "Ross S. W. Walker" <rwalker at medallion.com>
Reply-To: "Ross S. W. Walker" <rwalker at medallion.com>
Subject: RE: [DRBD-user] drbd implementation question
      To: kbyrd-drbd at memcpy.com, drbd-user at lists.linbit.com

> Kelly Byrd wrote:
>>
>> On Thu, 18 Oct 2007 18:48:56 +0200, "Rudi Ahlers"
>> <Rudi at SoftDux.com> wrote:
>> > Hi all
>> >
>> > I'm new to drbd and have some questions, hoping someone
>> could help me.
>> I'd
>> > like to use software RAID & LVM to make it easier to upgrade in the
>> future.
>> >
>>
>> > how do I manage such a setup?
>> > Do I first setup the RAID, then the LVM volumes and the drbd?
>> > Can I install & setup drbd on partitions with existing data?
>> >
>>
>> What are you looking for in the end? One big replicated chunk
>> of space? Do you need smaller granularity? For the local
>> RAID, what are the requirements there? RAID0? RAID5? RAID1?
>>
>> If you're going to run raid and lvm underneath drbd, I'm not
>> sure how you'll keep existing data. Wouldn't creating LVMs on
>> top of an  existing partition with data in it destroy that
>> filesystem?
>>
>> I'm pretty sure you can't directly create a drbd with existing
>> data,  drbd is a block device, so it would run underneath a
>> filesystem. If you had a filesystem with data in it already,
>> making a drbd out of that space would screw up the filesystem
>> and the data. Just like when you create a RAID1 from existing
>> data, you copy the data into the RAID1.
>
> Create the RAID, whether it is HW or SW.
>
> Create a LVM VG out of the RAID array(s).
>
> Create LVM LVs out of the VG.
>
> You can create a drbd volume after the fact, you just CANNOT
> create it with the meta-data on that volume you have to locate
> the meta-data on a separate volume.
>
> I prefer to locate the meta-data separately anyways, I create
> a separate LV for drbd meta-data, and do drbd per-LV instead
> of per RAID array.
>
> -Ross
>
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----- End message from rwalker at medallion.com -----

   Thanx for the input, Ross & Kelly

   Kelly, to answer your questions:

   * I'd use any level of RAID, depending on the application / use of  
the servers
   * I really only want to use LVM to make growing the partition size  
easier. But from what I can gather, I don't need to use LVM, is that so?

   Ross, I do have a question for you, on your suggestion.

   Let's say I have 2x 160GB HDD's, which I mirror RAID, leaving me  
with /dev/md1 (100MB) & /dev/md1 (158GB - rest = swap), now I create  
my LV volumes, / (/dev/mapper/system-root) being say 8GB, /home  
(/dev/mapper/system-home) being 100GB, and /opt  
(/dev/mapper/system-opt) 50GB. When I setup the partitions like this  
when I install the machine, all the relevant info is installed, so I  
need to temporarely move the info from /home & /opt somewhere else if  
I want to sync those to patitions?

   And, what do I add to my drbd.conf file for those parititions? I  
have tried /dev/mapper/system-home, but it doesn't seem to work. How  
do I use LVM VG's with DRBD?

   --

Kind Regards
Rudi Ahlers
SoftDux CEO

Website:     http://www.SoftDux.com
Support:      http://Support.SoftDux.com
Cellphone: 082 554 7532


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