Access existing hard disk?

[djbon2112]

Hello everyone. I'm new to virtualization and ProxMox in general, so please bear with me.

I've got my sever w/ProxMox (the latest one) configured with a single VM which is running Ubuntu Server 8.04 x86_64. Now, I have a RAID array that I use to serve my content, and it's currently half-full (so formatting or w/e is not an option). Is there a way to allow my single VM (as it will be the only one to ever have to access this) direct access to this drive?

 

[djbon2112]

Goodness me, I got to the wrong support forum when I didn't think I was in it! Would a moderator please move this post to a more appropriate forum?

 

[tom]

Hello everyone. I'm new to virtualization and ProxMox in general, so please bear with me.

I've got my sever w/ProxMox (the latest one) configured with a single VM which is running Ubuntu Server 8.04 x86_64. Now, I have a RAID array that I use to serve my content, and it's currently half-full (so formatting or w/e is not an option). Is there a way to allow my single VM (as it will be the only one to ever have to access this) direct access to this drive?

first, I moved the thread, your are welcome here.

second, please give more info about your RAID array. how is the raid array connected to your Proxmox VE server?

Currently Proxmox VE only supports one local storage for VM´s, configured automatically during installation. Upcoming versions (after 1.0) will support multiple storages, very flexible. see the roadmap.

 

[djbon2112]

It's a RAID5 array of 4 750GB disks on a Dell PERC 5/i. Though it seems that having only the one local storage is a major issue.

 

[djbon2112]

Is there a way to do this manually using the Qemu monitor? Reading their documentations seems to imply that you can.

 

[dietmar]

See the manual page for 'qemu-server' and 'qm'. You can control everything from the command line.

 

[clipcarl]

(Assuming you are talking about a KVM VM.)

You can attach the RAID array to the Proxmox VE server as you would any to any Linux box. Then edit the configuration file for your VM (/etc/qemu-server/xxx.conf) to include a line like this one:

ide1: /dev/disk/by-id/<ID of RAID array>

Of course if you attach it to your VM as a SCSI disk if you prefer but IDE works very well with KVM VMs.

 

[djbon2112]

(Assuming you are talking about a KVM VM.)

You can attach the RAID array to the Proxmox VE server as you would any to any Linux box. Then edit the configuration file for your VM (/etc/qemu-server/xxx.conf) to include a line like this one:

ide1: /dev/disk/by-id/<ID of RAID array>

Of course if you attach it to your VM as a SCSI disk if you prefer but IDE works very well with KVM VMs.

Thanks for the help guys. I just have one question: are there any disadvantages to using SCSI versus IDE for the VMs? Is it any slower/faster or more dangerous?

 

[tom]

Thanks for the help guys. I just have one question: are there any disadvantages to using SCSI versus IDE for the VMs? Is it any slower/faster or more dangerous?

For Windows guests IDE is more stable, SCSI for boot disks is known not to work for the current beta version. For Linux guests, I have no bad experience but I cannot say anything about performance differences.

As a rule, just use IDE as this looks stable. the only issue here, you cannot assign more than 4 IDE devices to a VM guest, but normally this not a problem.

 

[andrewg]

Theoretically SCSI would be quicker as the SCSI protocol has less overhead than IDE, in practice I don't think you will find a difference until you get into the very high end, and I don't know how using a VM affects it, obviously it will depend on the implementation as it is virtualizing the resource.
That said I have linux guests running both SCSI and IDE with no problems.

 

[andrewg]

Forgot to add, you can always test it pretty easily in a linux guest with:
hdparm -T
gives you cached read speed (testing maximum interface speed) and:
hdparm -t
which gives you sequential read speed from the actual disks.

 

[djbon2112]

(Assuming you are talking about a KVM VM.)

You can attach the RAID array to the Proxmox VE server as you would any to any Linux box. Then edit the configuration file for your VM (/etc/qemu-server/xxx.conf) to include a line like this one:

ide1: /dev/disk/by-id/<ID of RAID array>

Just one more thing...

I noticed that doing this:

scsiX: /dev/sda

... where sda is my RAID array, seems to work as well (or at least it displays the correct size of the array in my web management). Would this way work as well? I wanted to make sure before I went and actually did anything with it!

 

[clipcarl]

Just one more thing...

I noticed that doing this:

scsiX: /dev/sda

... where sda is my RAID array, seems to work as well (or at least it displays the correct size of the array in my web management). Would this way work as well? I wanted to make sure before I went and actually did anything with it!

Yes, that will work too if you really want to use SCSI instead of IDE. I doubt seriously if there is any performance benefit for using SCSI and I believe IDE is more stable in certain situations.

If your RAID array is hot-pluggable I would suggest that you use /dev/disk/by-id/<whatever> or /dev/disk/by-label/<whatever> unless you are absolutely sure that it will always be /dev/sda.

 

[djbon2112]

Yes, that will work too if you really want to use SCSI instead of IDE. I doubt seriously if there is any performance benefit for using SCSI and I believe IDE is more stable in certain situations.

If your RAID array is hot-pluggable I would suggest that you use /dev/disk/by-id/<whatever> or /dev/disk/by-label/<whatever> unless you are absolutely sure that it will always be /dev/sda.

Alright, I was just kinda using "SCSI" as a placeholder. The array is not hot-pluggable so I guess the /dev/sda works. Thanks!