Xen workshop

On January 2009, we held a workshop lectured by Conexa on Xen servers. During the course of the workshop we learned about the specifications and the architecture of our virtual machines server but also about logical volumes management and creating and managing xen virtual machines.

Day 1

Architecture and hardware specifications

• Quad-core Opteron AMD with 20GB ram and 2 TB RAID5 Physical Volume composed by 4x750GB enterprise-graded hard-drives,
• Suse Enterprise Server v10.2 with Xen Hypervisor installed,
• Network address at 192.168.20.125.

Logical volumes management

LVM architecture

Physical Volume (PV)

/dev/sda or /dev/sdb

Volume Group (VG)

/dev/sda/dados01

Logical Volume (LV)

/dev/sda/dados01/vmmrtsrv01

RAID types

There hardware RAID controllers and software RAID controllers. The latter aren't that worthy since all is lost when the mainboard fails. Hardware RAIDS are great, as long as the controller is a separate board from the mainboard. If not, if the mainboard fails and if you can't find exactly the same mainboard, byebye data. Conexa recommends <goto>3Ware RAID controller boards</goto>.

RAID 0

Striping. Good for performance. Terrible for data security. It writes data split accross an array of hard-drives. If one hard-drive fails all the data is lost. However writing speed and performance are excellent.

RAID 1

Duplicate. Good for security. Everything is mirrored as is in a second hard-disk. If one disk fails, then the data exists in the other hard-disk. Not storage capacity efficient: 2GB of raw capacity for 1 GB of data storage.

RAID 10

Striping + Duplicate. Good for security and for performance. Basically its a RAID 0 PV that is replicated. Thus, it requires two identical arrays of hard-drives. 2GB raw for 1GB data.

RAID 5

Redundant striping. Good for performance AND security. It's basically a RAID 0 BUT redundant information is stored along each file, so that if one hard-disk fails the system can still recover all the information. However, as the system grows in hard-drives, the probability that 2 hard-drives fail gets bigger. Best compromise for performance, security AND storage capacity. Ratios vary but we have a 4GB raw : 3GB data ratio.

RAID 50

Striping the redundant striping. Its basically a composition of a RAID 0 applied on top of RAID 5 PVs.

Hot swap

A hot swap hard-disk is a hard-disk left alone that you can readily change whenever one of the hard-disks fails. It's very convenient. Works best with RAID 1, 10, 5 or 50. Currently the Maretec xen server doesn't has any.

Creating and configuring new xen virtual machines

• Console access through a VNC client via 192.168.20.125:590?