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Tuesday, 24 February 2004 |
The other day I sent an email announcing downtime needed to reboot about 17 servers to complete installation of the latest round of security patches from Microsoft.
While mindlessly rebooting server after server, it occured to me the patch game has changed the uptime equation. Administrators used to worry about downtime due to system crashes, power outages, upgrades and so on. Now a server in perfect working order can be taken down by the discovery of a vulnerability and the ensuing release of a patch.
Microsoft recently adopted a policy of releasing patches on a monthly basis. They have already broken this policy at least once after the discovery of a particularly serious vulnerability. Assuming the best case scenario of patching once a month and each round of patches requiring only a single reboot that takes about ten minutes, the patch game adds 120 minutes of downtime per year to a system.
To put that in five nines perspective (99.999% reliability being the nirvana of system availability) the very best you could hope for is somewhere between 99.90% and 99.99% availability (99.977% to be exact, assuming 120 minutes of downtime). Three nines allows 525 minutes of downtime and four nines only 53 minutes.
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