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High Availability through Virtualization. Is RAID enough? Tomas Florian. Florien. Consulting Linux servers Windows workstation interoperability VPNs / Remote access .NET development. Summary. High Availability DRBD Failover Heartbeat Virtualization Xen vs VMWare Xen architecture
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High Availability through Virtualization Is RAID enough? Tomas Florian
Florien • Consulting • Linux servers • Windows workstation interoperability • VPNs / Remote access • .NET development
Summary • High Availability • DRBD • Failover • Heartbeat • Virtualization • Xen vs VMWare • Xen architecture • HA + Virtualization • Questions
High Availability : HA • Linux-ha.org project • Graceful degradation Better than:
Challenges • Replicate data • DRBD Network RAID-1 • Failover • Take over responsibilities from the dead peers • Automatically detect failure • Heartbeat node1 node2
Replicate Data: DRBD • Distributed Replicated Block Device • Network RAID-1 • One active drive (primary) • N spare drives replicated on the network in real-time • In case of primary HD failure, switch to one of the available secondary drives • Mount just like any other block device mount /dev/drbd0 /data
Failover : haresources • node1 running Apache • node2 running qmail • node1 dies … apache dies. Node 2: • Take over primary use of DRBD device • Take over IP • Take over Apache
Detect Failure: heartbeat • Ping through ethernet • Split brain • Ping through serial cable + ethernet • STONITH – Shoot The Other Node In The Head .. node2 is dead .. Time to takeover .. node1 is dead .. Time to takeover node1 node2
Example Apache qmail drbd0 drbd1 drbd0 drbd1 node1 node2 Active resources Backup resources
Example Apache qmail drbd0 drbd1 drbd0 drbd1 node1 node2 Active resources Backup resources Dead resources
Example Apache qmail drbd0 drbd1 drbd0 drbd1 node1 node2 Active resources Backup resources Dead resources
Example Apache qmail drbd0 drbd1 drbd0 drbd1 node1 node2 Active resources Backup resources Dead resources
Example Apache qmail drbd0 drbd1 drbd0 drbd1 node1 node2 Active resources Backup resources Dead resources
Example Apache qmail drbd0 drbd1 drbd0 drbd1 node1 node2 Active resources Backup resources Dead resources
Example Apache qmail drbd0 drbd1 drbd0 drbd1 node1 node2 Active resources Backup resources Dead resources
Example Apache Named mysql qmail drbd0 drbd1 drbd0 drbd1 node1 node2 Active resources Backup resources
Summary • High Availability • DRBD • Failover • Heartbeat • Virtualization • Xen vs VMWare • Xen architecture • HA + Virtualization • Questions
Xen • Pronounced ‘Zen’ • Open Source • Run multiple virtual machines on one physical machine • Like VMWare but different (better)
Setting up Xen • Install xen software on any Linux • Patch Domain-0 kernel • Boot to the new Domain-0 kernel • Deploy Domain-U virtual machines • Allocate disk • Deploy any distribution with a patched Domain-U kernel • …Or use a distribution that does this for you
Full Virtualization vs Paravirtualization • Paravirtualization • Needs kernel patch • Open source guest OS only (MS will not let you patch Windows kernel) • Full virtualization • Hypervisor implemented with VT CPUs • Windows on Xen possible
VT hardware • Intel • Vanderpool technology • Intel Pentium D • Intel Core Duo • AMD • Pacifica • Check that your BIOS also supports VT
VT support in Xen • 2.0.7 stable as a rock (but no VT) • 3.0.2 unstable (VT… almost) • People regularly report success running Windows guests … • … and crashes • Once v3 becomes stable it will be unstoppable
Summary • High Availability • DRBD • Failover • Heartbeat • Virtualization • Xen vs VMWare • Xen architecture • HA + Virtualization • Questions
No virtualization… MySQL samba named Apache qmail drbd0 drbd1 drbd0 drbd1 node1 node2 Active resources Backup resources
…with virtualization Web server Mail server Apache qmail MySQL named named drbd0 drbd1 drbd0 drbd1 node1 node2 Active resources Backup resources
Gains • Whole filesystem protection • / … not just /data • Simplified management • Manage failover for few machines rather than tens of services • No complicated syncing of updates or configuration on the nodes • Security: • If one service is hacked, only one VM is compromised
Pit falls • Performance • Running VMs more resource intensive than running daemons • Watch out for: • Virtual Memory thrashing • DRBD sync speed • HD performance • … going overboard • Don’t forget to backup
Resources • Linux High Availability Project • Linux-ha.org • Xen web site • Google search for “xen” • Xen Distributions • SuSE • FC5 • Xen Live CD • … or just compile on any 2.4.x - 2.6.x kernel • Paid support • www.florien.ca
Summary • High Availability • DRBD • Failover • Heartbeat • Virtualization • Xen vs VMWare • Xen architecture • HA + Virtualization • Questions