[DRBD-user] Problem with drbd and data alignment

Igor Cicimov icicimov at gmail.com
Tue Mar 28 11:32:07 CEST 2017

Note: "permalinks" may not be as permanent as we would like,
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On 28 Mar 2017 6:42 pm, "Marco Marino" <marino.mrc at gmail.com> wrote:

Hi Igor, you're right, I created the the partition on the client but I'm a
bit confused because I'm using /dev/drbd3 as a backstore for targetcli so
I'm expecting something like this:
sde
|------drbd3
             |----------drbd3p1
                               |------------------myvolgroup_lv1

instead of

sde
|---------sde1
|---------drbd3


Furthermore, I'd like to understand if I need to change my configuration or
it is ok for a production environment. The idea is that I need a drbd
device used as a backstores in targetcli and nothing else. I don't need to
resize it. On the initiator server I need to create a PV and then a VG and
many LVs. Actually I'm using a raw device as a backing device for drbd and
/dev/drbdX as a backstores. Let me know what do you think about this.


That is perfectly fine, single drbd device backed by a big block storage
exported as single lun over a target. Then a vg on the pv created from the
iscsi block device from which the lvs are created for the vm's. This is
fine for single vm host.

Thank you,
Marco





2017-03-27 23:40 GMT+02:00 Igor Cicimov <icicimov at gmail.com>:

>
>
> On 25 Mar 2017 8:16 pm, "Marco Marino" <marino.mrc at gmail.com> wrote:
>
> Hi, I'm trying to understand how to configure raw devices when used with
> drbd. I think I have a problem with data alignment. Let me describe my case:
>
> I have a raw device /dev/sde on both nodes and on top of it there is the
> drbd device. So, in the .res configuration file I have
> ....
> disk            /dev/sde;
> device          /dev/drbd2;
> ....
>
> At this point I used /dev/drbd2, *without create any partition,* as a
> backstore in the targetcli.
> On the iscsi initiator appeared one new device (/dev/sdf), and on top of
> it I create a new partition with type = LVM and finally a new PV, VG and
> many LVs.
> From the iscsi initiator it seems to be ok:
>
> [root at cv1 ~]# gdisk /dev/sdf
> GPT fdisk (gdisk) version 0.8.6
>
> Partition table scan:
>   MBR: protective
>   BSD: not present
>   APM: not present
>   GPT: present
>
> Found valid GPT with protective MBR; using GPT.
>
> Command (? for help): p
> Disk /dev/sdf: 7808351448 <(780)%20835-1448> sectors, 3.6 TiB
> Logical sector size: 512 bytes
> Disk identifier (GUID): D5C7161E-5C4C-42B3-BEDE-520DC049D106
> Partition table holds up to 128 entries
> First usable sector is 34, last usable sector is 7808351414
> <(780)%20835-1414>
> Partitions will be aligned on 2048-sector boundaries
> Total free space is 3221 sectors (1.6 MiB)
>
> Number  Start (sector)    End (sector)  Size       Code  Name
>    1            2048      7808350207 <(780)%20835-0207>   3.6 TiB
> 8E00  primary
>
> Command (? for help): q
> [root at cv1 ~]#
>
>
>
> The problem is on the drbd node where I have:
>
> [root at iscsi2 ~]# lsblk
> NAME                       MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINT
> ........
> sde                          8:64   0   3,7T  0 disk
> ├─sde1                       8:65   0   3,7T  0 part
> └─drbd2                    147:2    0   3,7T  0 disk
> [root at iscsi2 ~]#
>
> Futrhermore
>
> [root at iscsi2 ~]# gdisk /dev/sde
> GPT fdisk (gdisk) version 0.8.6
>
> Partition table scan:
>   MBR: protective
>   BSD: not present
>   APM: not present
>   GPT: present
>
> Found valid GPT with protective MBR; using GPT.
>
> Command (? for help): p
> Disk /dev/sde: 7808589824 <(780)%20858-9824> sectors, 3.6 TiB
> Logical sector size: 512 bytes
> Disk identifier (GUID): D5C7161E-5C4C-42B3-BEDE-520DC049D106
> Partition table holds up to 128 entries
> First usable sector is 34, last usable sector is 7808351414
> <(780)%20835-1414>
> Partitions will be aligned on 2048-sector boundaries
> Total free space is 3221 sectors (1.6 MiB)
>
> Number  Start (sector)    End (sector)  Size       Code  Name
>    1            2048      7808350207 <(780)%20835-0207>   3.6 TiB
> 8E00  primary
>
> Command (? for help): q
> [root at iscsi2 ~]#
>
>
>
>
> It seems that there are 2 "partitions" even though drbd2 is not a
> partition. Is this a problem related to my configuration?
>
>
> What do you mean 2 partitions? It is a partition on sde you created on the
> client and the drbd device itself. The lsblk shows you exactly that.
>
> My question is: how can I solve? Should I create a new partition on
> /dev/sde and use /dev/sde1 as a backing device for the drbd resource? Or
> perhaps should I create a partition on top of /dev/drbd2 before I can use
> the device as a backstore in targetcli??
>
> Thank you,
> Marco
>
>
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>
>
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