Migrating RAID 1 volumes to Dual ported disks.

Migrating RAID 1 volumes to Dual ported disks.

[Simon Jackson]

Hi.

I am currently using SATA drives in a RAID 1 configuration.  I am looking to use SAS drives instead of SATA.  As my first experiment I have plugged my SAS drive into a system and I have noticed that Linux sees the individual ports on the device as separate devices, so I have /dev/sdc and /dev/sdd which are both the same physical device.

So if I have a system with 2 SAS drives I am going to have 4 devices representing the two physical drives.  So my question is how do I create RAID 1 sets for partitions on these types of drive?  

My existing system carves 3 RAID 1 volumes from a pair of drives.  How do I translate this to the dual port SAS devices? 

Thanks Simon.

Re: Migrating RAID 1 volumes to Dual ported disks.

[Goswin von Brederlow]

Simon Jackson <sjackson@bluearc.com> writes:

> Hi.
>
> I am currently using SATA drives in a RAID 1 configuration.  I am looking to use SAS drives instead of SATA.  As my first experiment I have plugged my SAS drive into a system and I have noticed that Linux sees the individual ports on the device as separate devices, so I have /dev/sdc and /dev/sdd which are both the same physical device.
>
> So if I have a system with 2 SAS drives I am going to have 4 devices representing the two physical drives.  So my question is how do I create RAID 1 sets for partitions on these types of drive?  
>
> My existing system carves 3 RAID 1 volumes from a pair of drives.  How do I translate this to the dual port SAS devices? 
>
> Thanks Simon.

You would set up multipath to combine the two paths to the same disk
as a single device and then run raid over that.

MfG
        Goswin

RE: Migrating RAID 1 volumes to Dual ported disks.

[Simon Jackson]

Sorry, I am probably being thick here, but do you mean something like:

mdadm --create /dev/md10 --level=multipath --raid-devices=2 /dev/sdc /dev/sdd

When I tried this I got:

# mdadm --create /dev/md10 --level=multipath --raid-devices=2 /dev/sdc /dev/sdd
mdadm: /dev/sdc is too small: 0K
mdadm: create aborted
#



-----Original Message-----
From: goswin-v-b@web.de [mailto:goswin-v-b@web.de] 
Sent: 03 November 2009 19:32
To: Simon Jackson
Cc: linux-raid@vger.kernel.org
Subject: Re: Migrating RAID 1 volumes to Dual ported disks.

Simon Jackson <sjackson@bluearc.com> writes:

> Hi.
>
> I am currently using SATA drives in a RAID 1 configuration.  I am looking to use SAS drives instead of SATA.  As my first experiment I have plugged my SAS drive into a system and I have noticed that Linux sees the individual ports on the device as separate devices, so I have /dev/sdc and /dev/sdd which are both the same physical device.
>
> So if I have a system with 2 SAS drives I am going to have 4 devices representing the two physical drives.  So my question is how do I create RAID 1 sets for partitions on these types of drive?  
>
> My existing system carves 3 RAID 1 volumes from a pair of drives.  How do I translate this to the dual port SAS devices? 
>
> Thanks Simon.

You would set up multipath to combine the two paths to the same disk
as a single device and then run raid over that.

MfG
        Goswin

Re: Migrating RAID 1 volumes to Dual ported disks.

[Goswin von Brederlow]

Simon Jackson <sjackson@bluearc.com> writes:

> Sorry, I am probably being thick here, but do you mean something like:
>
> mdadm --create /dev/md10 --level=multipath --raid-devices=2 /dev/sdc /dev/sdd
>
> When I tried this I got:
>
> # mdadm --create /dev/md10 --level=multipath --raid-devices=2 /dev/sdc /dev/sdd
> mdadm: /dev/sdc is too small: 0K
> mdadm: create aborted
> #

If sdc is 0k big then it doesn't look like that is your full disk.

MfG
        Goswin