On 4/1/09 9:54 AM, "Scott Marlowe" <scott.marlowe@xxxxxxxxx> wrote: > On Wed, Apr 1, 2009 at 10:48 AM, Stef Telford <stef@xxxxxxxxx> wrote: >> Scott Marlowe wrote: >>> On Wed, Apr 1, 2009 at 10:15 AM, Stef Telford <stef@xxxxxxxxx> wrote: >>> >>>> I do agree that the benefit is probably from write-caching, but I >>>> think that this is a 'win' as long as you have a UPS or BBU adaptor, >>>> and really, in a prod environment, not having a UPS is .. well. Crazy ? >>>> >>> >>> You do know that UPSes can fail, right? En masse sometimes even. >>> >> Hello Scott, >> Well, the only time the UPS has failed in my memory, was during the >> great Eastern Seaboard power outage of 2003. Lots of fond memories >> running around Toronto with a gas can looking for oil for generator >> power. This said though, anything could happen, the co-lo could be taken >> out by a meteor and then sync on or off makes no difference. > > Meteor strike is far less likely than a power surge taking out a UPS. > I saw a whole data center go black when a power conditioner blew out, > taking out the other three power conditioners, both industrial UPSes > and the switch for the diesel generator. And I have friends who have > seen the same type of thing before as well. The data is the most > expensive part of any server. > Yeah, well I¹ve had a RAID card die, which broke its Battery backed cache. They¹re all unsafe, technically. In fact, not only are battery backed caches unsafe, but hard drives. They can return bad data. So if you want to be really safe: 1: don't use Linux -- you have to use something with full data and metadata checksums like ZFS or very expensive proprietary file systems. 2: combine it with mirrored SSD's that don't use write cache (so you can have fsync perf about as good as a battery backed raid card without that risk). 4: keep a live redundant system with a PITR backup at another site that can recover in a short period of time. 3: Run in a datacenter well underground with a plutonium nuclear power supply. Meteor strikes and Nuclear holocaust, beware! -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
