Greg Whalin wrote:
Many data centers do not allow customers to install their own UPS inside the rack. I am not sure if this is the case with Wikipedia, but it is definitely the case at the data center we are hosted in. I would love to shove one in after reading the horror stories at Livejournal and now Wikipedia.
I see.
Do the data centers offer their own UPS ( as opposed to the customer setting up one for themselves ), or do they simple ban the use of UPSs outright?
Either way, if you *need* a UPS, you can't hide behind the excuse "oh yeah but XYZ wouldn't let me". You find a way to make it happen ... or if you can't you at least don't start blaming your software for what is obviously a hardware issue.
Our data center spans two power grids, has a massive battery backup, and is backed by two massive generators, making power loss pretty difficult.
However, we once lost power to our entire cage by hooking into too many servers into a single circuit and tripping a breaker. We now have two power feeds coming into each rack, and redundant power supplies on each db server split between the two circuits. We also carefully watch our power utilization to make sure we don't come close to hitting this limit.
As I understand it, both LJ and Wiki suffered from someone hitting EPO switch (emergancy power off used to kill all power for when fire fighters have to come through ... a safety to make sure the firemen are not electrocuted when putting out fires). This EPO switch is precisly why UPSs are sometimes not allowed in each individual rack. For safety reasons, they need to ensure that all power is off in event of fire/rescue crews having to come through.
I am not sure that LJ or Wiki blamed mysql. In fact, the only mysql complaint I saw from LJ was that they had to spend time rebuilding index files for their few remaining myisam tables. This I can easily believe as I see myisam indexes get corrupted when I sneeze in their general direction. However, LJ mentioned that all of their innodb tables recovered with no problems. In fact, both Wiki and LJ mentioned drive write caching to be the major cause of their problems.
Greg -- [EMAIL PROTECTED] Meetup.com
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