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Re: Linux filesystems was [Re: Debian cd supporting ext4.]

Aniruddha put forth on 7/27/2010 9:43 AM:
> On Tue, Jul 27, 2010 at 3:22 PM, Volkan YAZICI <yazicivo@ttmail.com> wrote:
>> You are missing a very important point: Durability to power failures.
>> (Excuse me, but a majority of GNU/Linux users are not switched to a UPS
>> or something.) And that's where XFS totally fails[1][2].
> Ext3 has the same problems when not properly configured:
> Ext3 does not do checksumming when writing to the journal. If barrier=1 is
> not enabled as a mount option (in /etc/fstab), and if the hardware is doing
> out-of-order write caching, one runs the risk of severe filesystem
> corruption during a crash.
> http://en.wikipedia.org/wiki/Ext3#No_checksumming_in_journal
> For the record I use ext3, I remember XFS as not being reliable enough
> (with power failures etc).

This isn't a filesystem problem, or a kernel problem, or any other technical
problem.  This is a user problem.  You will _never_ get computing technology
the fully does what you _think_ it should upon loss of power.  Period.  XFS
will prevent filesystem corruption (lookup the definition) but it will not
prevent data loss.  These are two completely different things.  _No_
filesystem will fully prevent data loss when power is lost, but most will
prevent filesystem corruption.  Again, these are two different things.

If you want maximum performance, you have to enable drive caches.  Doing so
causes more data loss when the power goes, and again, it's not the fault of
the filesystem.  If you want maximum protection against data loss, you have to
disable drive caches, reduce the size of the in memory journal log buffer,
etc, etc.  Doing all of these things will absolutely murder your FS
performance.  This is a balancing act folks.  You can't have your cake and eat
it too.

I'd also like to add that anyone smart enough to be on this list is smart
enough to know you should have a UPS, regardless of what filesystem you use.
If you're not you shouldn't be here.  If you disagree on the technical merits
(not cost), you're uneducated and/or stubborn.  If you disagree on a cost
basis, your data isn't valuable, period.  A decent low end UPS for a desktop
system that will get you through all brown outs and far enough through a storm
outage (15-30 minutes) to do a proper shutdown costs about $50 USD.  That's
less than a carton of cigarettes in New York City, less than 3 regular price
large pizzas at Dominos, and $25 less than a tank of gas for a full size
pickup, which would last most people one week of commute.  The cost of one
tank of gas for 3-5 years of power protection before needing a battery

I guess I should evangelize UPS as much as XFS given the benefits.  Except XFS
is free. ;)


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