virt February 2010

virt@lists.centos.org

33 participants
27 discussions

Best practices for LVM and virtualization
by Mathieu Baudier 10 Feb '10

10 Feb '10

Hello, I'm currently setting up a virtualization infrastructure based on CentOS 5.4 x86_64 and KVM. I want to use LVM because of its flexibility, especially the ability to add more disk space to a guest if needed. We are considering using an hardware RAID1 with BBU as the lowest layer. My question is: where is it recommended to put the LVM? 1. On the host only In that case, the guests would see logical volumes as hard drives and would be installed with "plain" partitions (ext3 / swap) When more space is needed the logical volume (from host perspective) / drive (from guest perspective) would simply become bigger. This feels simple, but I wonder whether there may be side effects, since real harddrive cannot grow, and maybe some parts of the system expect them to stay of a given size. 2. On the guest only On the host, there would only be "plain" raw partitions, which the guest would see as hard drives. The guest would be installed with an LVM and when more space is needed, an additional partition (from host perspective) / drive (from guest perspective) would be added to the guest volume group, which would then become bigger, allowing logical volumes to grow. I'm not too comfortable with that, since my understanding of the role of the host is to manage resources for the guests: memory, CPUs so I'd like to have some powerful abstraction there for disk space as well, which is one purpose of LVM. The guest would then need to be restarted when space is added. 3. On both host and guest LVM would be installed on the host, which would then provide the logical volumes as hard drives for the guest. The guest would use them as additional drives to be added to its own volume group when it needs to grow. This feels the most flexible, but I wonder whether it is not wrong to add LVM layers upon LVM layers, from a performance/stability/simplicity perspective. The guest would probably have to be restarted when more space is needed (I've not tested this extensively yet) I would be very interested to have your opinion / experience about this before I go further in my testing! Cheers, Mathieu

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Re: [CentOS-virt] Can I use direct attached storage as a shared filesystem in Xen
by Christopher G. Stach II 09 Feb '10

09 Feb '10

----- "Rich" <rhdyes(a)gmail.com> wrote: > I am doing rsync now. What is the difference between ocf2 and gfs? There are comparisons on the web, but in short, cluster size, GFS can be a major pain in the ass for some people to set up (fencing support is usually said pain), and GFS has distribution support. For such a small installation, you are probably better off with OCFS2. If you need something that is almost exactly the same as a local filesystem and depend upon certain filesystem behaviors for whatever reason (locking comes to mind), you will be better off with GFS. -- Christopher G. Stach II http://ldsys.net/~cgs/

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Re: [CentOS-virt] Can I use direct attached storage as a shared filesystem in Xen
by Christopher G. Stach II 09 Feb '10

09 Feb '10

----- "Rich" <rhdyes(a)gmail.com> wrote: > I think the better question is this. How can I make my 2 physical > servers that are identical into the best clustered solution sharing > the storage between the 2. Do you want the storage to be redundant between the two like RAID 1 or just all of it accessible to any guest on either machine like a JBOD? For either, you can use a suitable mix of drbd, iSCSI, GNBD, LVM, heartbeat, keepalived, and a clustered filesystem. If you do the latter, remember that this squares your risk. If you want a simple A/B failover setup where the second physical host is idle until the first physical host fails, you can just use drbd and heartbeat or RHCS. > They all use xfs. > I want to keep the guests the same on each server. > I will start with the backup server. I will go on each vm and delete > this FS and block device. > I then want make that whole 10 terabyte raid into one gfs and then > re-attach it back to each guest. > Is that possible or do I have to start all over again? If it can be > done I then will sync the date from the mainserver to this backup > server and then switch them and do the same to the mainserver. That sounds about right. You need to make your backups (!), destroy the data on of your servers by creating the new clustered filesystem, copy the data from the other server, and then share it with your reconfigured guests. So, basically what you said. > I have one more question which is another whole thread. > I am using rsync to sync the 2 physical boxes now. Is there a better > way to do this? drbd, but rsync does a pretty good job in a lot of use cases. I wouldn't say that it fits this one, though. -- Christopher G. Stach II http://ldsys.net/~cgs/

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Re: [CentOS-virt] Can I use direct attached storage as a shared filesystem in Xen
by Christopher G. Stach II 09 Feb '10

09 Feb '10

----- "Adam Adamou" <adam0x54(a)gmail.com> wrote: > either nfs or ocfs2. nfs is the easiest route. ocfs2 will give you a > clustered filesystem. Except NFS doesn't follow normal filesystem semantics and you can end up with corrupt data without knowing it, and it, along with CIFS, will give you a free shitload of network overhead to go along with your possibly corrupt data. OCFS2 or GFS are the only practical choices if you want it to behave like a typical filesystem and not have to worry about catering to it or rewriting software and/or reeducating developers, and OCFS2 is extremely easy to set up. The original question didn't specify much about the requirements, though. A single shared filesystem? Read-write or read-only? No filesystem at all? Without that information, I would at first recommend not sharing. It can be a lot of trouble, it's usually not required, and it severely complicates life when things fail. Well, there is always XenFS... :/ -- Christopher G. Stach II http://ldsys.net/~cgs/

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Can I use direct attached storage as a shared filesystem in Xen
by Rich 08 Feb '10

08 Feb '10

I have a quad core server in which I want to run 4 virtual servers. On this server I have a 1/2 terabyte raid 1 I have split between the 4 members that have the OS on it. I have raid 5 10 terabyte internal storage running on a 3ware 9690a card. I want to share this storage between the servers without partitioning it. Is this possible?

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Re: [CentOS-virt] Fault Tolerance
by Christopher G. Stach II 01 Feb '10

01 Feb '10

----- "Gilberto Nunes" <gilberto.nunes32(a)gmail.com> wrote: > Well... > > I mean two host, when one fault the other take the place.... Red Hat Cluster Suite has been available since RHEL 2.1. If you are talking about checkpoint-restart, program state replication, lockstep, etc., no. As far as I know, that's only available with things that are outside of the context of this list. -- Christopher G. Stach II http://ldsys.net/~cgs/

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Fault Tolerance
by Gilberto Nunes 01 Feb '10

01 Feb '10

Hi people... I want know if Source Codes Virtulization Solution from Red Hat has be release? Thanks -- Gilberto Nunes

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virt February 2010