[NTLUG:Discuss] ext3 vs. XFS vs. ....

[Leroy Tennison]

Robert Pearson wrote:
> On 5/2/06, Mike Hart <just_mike_y at yahoo.com> wrote:
>   
>> Speed, disk space, and cpu usage don't mean much when
>> you get multipe power outages spaced about 30-40
>> seconds apart, just long enough for the drive to be in
>> the process of a forced filesystem check during boot.
>>
>> Where's the benchmark on reliability? Specifically on
>> a killswitch during a fschk after a kill. I'd be
>> really interested to see how the different filesystems
>> standup to our powergrid in spring :-)
>>     
>
> I have read Burton's reply and agree with it.
> The filesystem can never be the first line of defense against power
> outages. The worst case of which is the one you mention, whipsawing.
> I have seen file system corruption in cases where the system was
> fully up and had been operating for some time, and a "whipsaw"
> condition occurred such that the power did not go completely off.
> The disks never spun down. Talk about a mess. Hardware failures
> above the filesystem can totally destroy the file system through
> corruption.
> About the best a filesystem in an unstable power situation can
> do is either shutdown and refuse to come up until the power
> is stable or be able to come up in less than 5 seconds and
> "checkpoint" every ".1" seconds. This means it could recover to
> within any ".1" second increment of the boot or recovery.
> To "checkpoint" at anytime the remainder of the hardware the
> file system relies on must be stable. All bets on this are off in
> a power whipsaw without line power conditioning and a UPS.
> A UPS may not be sufficient to handle power whipsaws. In areas of
> high whipsawing, which could be caused by industrial areas,
> bad wiring, or high lightening strikes, a top quality UPS coupled
> with a line power conditioning transformer would be a "must have"
> configuration.
> The best overall fault tolerant box I ever saw was Tandem.
> We used to try everything in the world to make them stop.
> The best fault tolerant filesystem was on the Sequoia platform.
> It was a beauty. It had so many wonderful features. I loved that
> machine.
> Stratus was (is?) a good price/performance box. It was best
> at hardware failure failover, like CPUs, when I used them.
> A power whipsaw could put a Stratus out of business in the
> filesystem. We ran all of ours on a UPS.
> All of these machines were (are?) really expensive.
> Today, superior fault tolerance to these machines can be
> provided, for much less cost, with redundancy.
> Caveat! If you cheapen the hardware platforms too much then
> the redundancy doesn't buy you anything for hardware failure
> failovers.
> For example, don't use a Desktop PC mobo for cluster servers.
> Use a good quality Server PC mobo. It will be well worth the
> extra money, about 2x the Desktop mobo, if the Information
> you are trying to protect is worth anything.
> At least SATA disks for the primary mirrors. SAS preferred
> with at least SATA in the secondary.
> IDE in the tertiary and quaternary mirrors. Three "nines" of
> Information High Availability is good enough in the third and
> fourth mirrors. Provided you do regular, "good" backups for
> Disaster Recovery.
>
> _______________________________________________
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>
>   
I was wondering when we were going to get around to this, the "defense" 
against a whipsaw condition is to not have it (at least not have it show 
up at the computer).  If power is that bad in a location maybe it's time 
to consider alternatives such as moving or renting space somewhere else 
to keep the computer.

Another curious, wild thought came to mind.  Anyone know how expensive 
it would be to have an electric motor coupled to a generator via a 
relatively large/dense cylinder such that the computer was totally 
isolated from the external electrical environment?