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DRBD and RAID-1

 

 

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ci at sikkerhed

Nov 30, 2009, 6:10 AM

Post #1 of 3 (683 views)
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DRBD and RAID-1

Hello DRBD-users

We have been using DRBD for nearly a year now, and have enjoyed the many
benifits of it tremendously.

However, we are trying to set up a new set of DRBD-enabled servers with
slightly higher performance.

We especially need read performance and higher seek performance, so we
want to go with a RAID-1 on the primary server. We are aware that DRBD
can't go faster than the slower of the two servers, but since the
secondary server only needs to replicate the writes, this is not an
issue for us, I believe.

The setup we want is the following:

Primary:
2 x 1.5TB SATA in RAID-1 (/dev/md1 (sda2, sdb2))

Secondary:
1 x 1.5TB SATA (/dev/sdb2)

DRBD:
1 x 1.5TB (/dev/drbd1 from /dev/md1(pri) and /dev/sdb(sec))

Seems to work fine. However, we would like to use LVM on top of the DRBD
disk. When I issue the pvcreate command, it works, but pvdisplay gives
me the following:

# pvcreate -vv /dev/drbd1
Setting global/locking_type to 1
File-based locking selected.
Setting global/locking_dir to /var/lock/lvm
Locking /var/lock/lvm/P_orphans WB
/dev/drbd1: No label detected
/dev/drbd1: size is 2914640640 sectors
metadata/pvmetadatasize not found in config: defaulting to 255
metadata/pvmetadatacopies not found in config: defaulting to 1
/dev/drbd1: size is 2914640640 sectors
Set up physical volume for "/dev/drbd1" with 2914640640 available
sectors
Scanning for labels to wipe from /dev/drbd1
Zeroing start of device /dev/drbd1
Writing physical volume data to disk "/dev/drbd1"
/dev/drbd1: Writing label to sector 1
Physical volume "/dev/drbd1" successfully created
Unlocking /var/lock/lvm/P_orphans


# pvdisplay /dev/drbd1
"/dev/md1" is a new physical volume of "1,36 TB"
--- NEW Physical volume ---
PV Name /dev/md1
VG Name
PV Size 1,36 TB
Allocatable NO
PE Size (KByte) 0
Total PE 0
Free PE 0
Allocated PE 0
PV UUID cRN1vb-T3pe-x85L-Ww0I-9DXf-7cSF-d6PAzW

Yes, you read that right. It says /dev/md1. At this point I'm not sure
if this is a minor naming bug, or a major data corruption bug? I'm sure
that if the device is changed without updating the metadata, it will
potentially destroy data.


Can anybody explain this? I sure looks like a bug in the block layer,
but is it related to DRBD? Or is is entirely benign?

--
Med venlig hilsen / Best regards
Christian Iversen

Sikkerhed.org ApS
Fuglebakkevej 88 E-mail: support [at] sikkerhed
1. sal Web: www.sikkerhed.org
DK-2000 Frederiksberg Direkte: ci [at] sikkerhed
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nine at detonation

Nov 30, 2009, 7:30 AM

Post #2 of 3 (655 views)
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Re: DRBD and RAID-1 [In reply to]

On Monday 30 November 2009 15:10:45 Christian Iversen wrote:

> Seems to work fine. However, we would like to use LVM on top of the DRBD
> disk. When I issue the pvcreate command, it works, but pvdisplay gives
> me the following:
>
> Yes, you read that right. It says /dev/md1. At this point I'm not sure
> if this is a minor naming bug, or a major data corruption bug? I'm sure
> that if the device is changed without updating the metadata, it will
> potentially destroy data.
>
>
> Can anybody explain this? I sure looks like a bug in the block layer,
> but is it related to DRBD? Or is is entirely benign?

It has already been explained pretty well in the DRBD user's guide:
http://www.drbd.org/users-guide/s-lvm-drbd-as-pv.html

Regards,
Stefan
Attachments: signature.asc (0.19 KB)


andreas.haase at evolver

Nov 30, 2009, 7:30 AM

Post #3 of 3 (650 views)
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Re: DRBD and RAID-1 [In reply to]

Hi,

Am Montag, den 30.11.2009, 15:10 +0100 schrieb Christian Iversen:
> Yes, you read that right. It says /dev/md1. At this point I'm not sure
> if this is a minor naming bug, or a major data corruption bug? I'm
> sure that if the device is changed without updating the metadata, it
> will potentially destroy data.

that has nothing to do with DRBD. You only have to change your LVM
filter settings to only look for LVM signatures on /dev/drbd*.
--
Mit freundlichen Gruessen

Andreas Haase

Administration und Technik
evolver services GmbH

Fon +49 / (0)3 71 / 4 00 03 727
Fax +49 / (0)3 71 / 4 00 03 79

E-Mail andreas.haase [at] evolver
Web http://www.evolver.de


Sitz der Gesellschaft: Chemnitz
Handelsregister: Amtsgericht Chemnitz, HRB 22649
Geschaeftsfuehrer: Dirk Neubauer

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