Thursday Dec 19, 2013

Next Virtual Sysadmin Day Is On Jan 28

OTN's next virtual sysadmin day is on January 28. It's four hours long, from 9:00 am - 1:00 pm PT. (Time converter here.) This time we have a whole new set of hands-on labs for Oracle Solaris, Oracle Linux, and Oracle VM. Proctored, of course, which means you can ask questions. The labs in our previous virtual sysadmin day focused on the basics. These focus on using these technologies in real-world scenarios. Click on the Agenda tab in the registration page to see the labs.

The event is free, but you do need to register. And there's a little homework involved. Nothing too complicated. We just expect you to have VirtualBox installed and the proper images already imported before we begin class. Click on the the Instructions tab for more info.

Register here.

Picture is of Mosquito Pass, in Colorado, taken from Mosquito Gulch. You need a 4x4 with good ground clearance to get up and over the top, and the rocks on the road will slice up your tires unless they're good and thick. A great place to catch your breath after you finish the hands-on labs.

- Rick

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Friday Feb 15, 2013

Sysadmins Rejoice! OVM 3.2.1 Includes a Full-Featured CLI

Remember this famous scene from English History? The French accent of the castle guard was so thick I couldn't understand him, but I think that at one point he said "I spit on your graphical user interface." Proof that sysadmins were alive and well in the time of King Arthur.

CLI Documentation

Sysadmins will have cause to taunt English royalty a second time because the command line interface (CLI) of the recently released Oracle VM 3.2.1 has been expanded to include all the capabilities of the (ptui!) graphical user interface (GUI). That means scripts. Boo-yah! It supports public-key authentication, too. Find docs here.

Other Cool Stuff

Oracle VM Manager used to manage only your x86 virtual machines. Now it manages your SPARC systems, too. Create server pools, create virtual machines, and manage networking and storage in the same way, using the same tool. Details here.

You can use MySQL as your backend repository. Just use the Simple installation, which will locally install the default MySQL database that is packaged with the Oracle VM Manager installer. Details here.

You can install the osv-support-tools meta-package for easier integration with Oracle support tools. (sudo is now part of osv-support-tools.) Details here.

More Resources

- Rick

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Wednesday Jan 09, 2013

How to Treat an NFS File As a Block Storage Device

source

Wim actually beat me in blogging about this feature while I was on vacation, but I'd like to add a little more background about dm-nfs, which I gathered from our kernel developers:

What is dm-nfs?

The dm-nfs kernel module provides a device-mapper target that allows you to treat an NFS file as a block device. It provides loopback-style emulation of a block device using a regular file as backing storage. The backing file resides on a remote system and is accessed via the NFS protocol.

The general idea is to have a more-efficient-than-loop access to files on NFS. The device mapper module directly converts requests to the dm device into NFS RPC calls.

dm-nfs is used transparently by Oracle VM's Dom0 when mounting NFS-backed virtual disks. It essentially allows for asynchronous and direct I/O to an NFS-backed block device, which is a lot faster than normal NFS for virtual disks. The Xen block hotplug script has been modified on OVM to look for files which are on NFS filesystems. If the file is on NFS, OVM uses dm-nfs automatically, otherwise it falls back to using the regular (but slower) loop mount method.

The original dm-nfs module was written by Chuck Lever. It has been supported and used by Oracle VM since version 2.2 and is also included in the Unbreakable Enterprise Kernel for Oracle Linux.

Why this feature matters

This feature creates virtual disk devices (LUNs) where the data is stored in an NFS file instead of on local storage. Managed networked storage has many benefits over keeping virtual devices on a disk local to the physical host.

A sample use case is the fast migration of guest VMs for load balancing or if a physical host requires maintenance. This functionality is also possible using iSCSI LUNs, but the advantage of dm-nfs is that you can manage new virtual drives on a local host system, rather than requiring a storage administrator to initialize new LUNs on the storage subsystem. Host administrators can handle their own virtual disk provisioning.

For durability and performance, dm-nfs uses asynchronous and direct I/O so all I/O operations are performed efficiently and coherently. Guest disk data is not double cached on the underlying host. If the underlying host crashes, there's a lower probability of data corruption. If the guest is frozen, a clean backup can be taken of the virtual disk, as you can be certain that its data has been fully written out.

How to use it

You use dm-nfs by first loading the kernel module, then using dmsetup to create a device mapper device on your file. The syntax is very similar to the dm-linear module.

The following sample code demonstrates how to use dmsetup to create a mapped device (/dev/mapper/$dm_nfsdev) for the file $filename that is accessible on a mounted NFS file system:

nblks=`stat -c '%s' $filename`
echo -n "0 $nblks nfs $filename 0" | dmsetup create $dm_nfsdev

Now you can mount /dev/mapper/$dm_nfsdev like any other filesystem image.

- Lenz Grimmer (Oracle Linux Blog)

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