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drbd-user: Re: [DRBD-user] Detection of Logical Volume on nested

Re: [DRBD-user] Detection of Logical Volume on nested LVM

From: Olivier LAMBERT <lambert.olivier_at_nospam>
Date: Sun Mar 07 2010 - 16:21:12 GMT
To: Maros Timko <timkom@gmail.com>

Hello,

cLVMdoesn't provide snapshots :(

But you say my behaviour is "normal" ?so, why lvcreate/lvremove is
not replicated ?it's not a "block" operation for the bottom layer ?
And if Iexport a physical volume (and not a LVMone) and then after
on iSCSI volume Ido "lvcreate" does it solve the problem ?

Regards,

Olivier
XO Project
http://xen-orchestra.com

On Sat, Mar 6, 2010 at 6:01 PM, Maros Timko <timkom@gmail.com> wrote:
>>
>> Message: 1
>> Date: Thu, 4 Mar 2010 17:48:24 +0100
>> From: Olivier LAMBERT <lambert.olivier@gmail.com>
>> Subject: [DRBD-user] Detection of Logical Volume on nested LVM
>> replication
>> To: drbd-user@lists.linbit.com
>> Message-ID:
>> <f769216c1003040848m4b1ffaaatc15dc952781ce946@mail.gmail.com>
>> Content-Type: text/plain; charset=ISO-8859-1
>>
>> Hello,
>>
>> I'll try to be clear, but it's really hard to explain..
>> In few words : when I create a Logical Volume on a host attached
>> (iSCSI) to one DRBD server, it doesn't appear on the second host,
>> attached to the other DRBD. But, on existing LV, it works like a charm
>> (all data's are replicated). And more, if I create a LV on "one side",
>> and fill it with data, I saw the replication link with heavy traffic,
>> but always no LV.
>> Now, to understand, here is how it happened with this infrastructure.
>>
>> 1) On both DRBD hosts : Debian GNU/Linux, Dual Primary setup, version:
>> 8.3.7 (api:88/proto:86-91). I choose to configure a resource on a
>> Logical volume of 500Gb (named /dev/vg0/xen). To be clear, two hosts
>> are "DRBD1" & "DRBD2". a cat /proc/drbd gave this :
>> 0: cs:Connected ro:Primary/Primary ds:UpToDate/UpToDate C r----
>> ns:153716 nr:408752 dw:562408 dr:355156 al:179 bm:109 lo:0 pe:0
>> ua:0 ap:0 ep:1 wo:n oos:0
>>
>>
>> 2) This resource is exported with iSCSI. For the example, let's say
>> that CLIENT1 is connected to DRBD1, and CLIENT2 is connected to DRBD2.
>> It's simplifed because in real, it's multiple Xen Dom0's clients with
>> multipath (but we don't care of that here).
>>
>> 3) CLIENT1 see the device as a block device (so far so good, iSCSI
>> works). I choose to use LVM on this block device. I create for example
>> : /dev/vg_xen/mydisk on CLIENT1. I mount it, I put some stuff in there
>> : I saw the replication like working : some traffic. DRBD2 and 1 says
>> it's all OK. If I lvscan on CLIENT1, I can see my brand new volume.
>>
>> 4) CLIENT2, (so, connected on iSCSI with DRBD2), see the block device,
>> the volume group, but NOT the Logical Volume. If I disconnect DRBD2's
>> resource, and reconnect it, and reconnect iSCSI of CLIENT2, wow, I saw
>> the LV !
>>
>> And more : if the LV exists on both side (after disconnect/reconnect
>> the resource), data's are correctly replicated (obviously, I do NOT
>> mount LV on both side, I'm aware of that !). But, if I fill on one
>> side (e.g CLIENT1), dismount it, then mount it on CLIENT2, data are
>> here, without any problem.
>>
>> So, my "theory", is that LVM operations (lvcreate or lvremove) on a
>> volume group, which is on top of iSCSI and LVM replicated device by
>> DRBD, are NOT replicated, UNTIL disconnect/reconnect the ressource. I
>> don't know why, and that's why I ask here to understand what I miss.
>
> Right. Discussed many times here and on Heartbeat/Pacemaker list. Try
> to search with cLVM keyword.
>
>> Additional Informations: If my clients are connected to the SAME DRBD
>> (let's tell DRBD1), if CLIENT1 creates a LV, CLIENT2 is immediatly
>> aware of that (just inactive, not a problem, vgchange and it works).
>> So the "problem" is during the replication.
>>
>> Thanks for your help.
>>
>>
>> Regards,
>>
>>
>> Olivier
>> XO Project
>> http://xen-orchestra.com
>>
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