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Re: XFS fs size limit?

Subject: Re: XFS fs size limit?
From: yocum@xxxxxxxx
Date: Fri, 03 Aug 2001 14:07:41 -0500
Cc: xfs-list <linux-xfs@xxxxxxxxxxx>
References: <200108021734.f72HYDo07108@jen.americas.sgi.com> <4.3.2.7.2.20010802224302.03e82e68@pop.xs4all.nl> <4.3.2.7.2.20010802231931.03d33168@pop.xs4all.nl>
Sender: owner-linux-xfs@xxxxxxxxxxx
Seth Mos wrote:
> 
> At 15:00 2-8-2001 -0600, Steve Wolfe wrote:
> > > >I assume you mean software RAID5, right?  I've got a RAID50 array: 
> > > >28-port
> > > >3ware cards in hw raid5, then those two devices combined softwareraid0.  
> > > >I
> > > >didn't bother to make the log on a separate device, but I could,
> > ifneed be.
> > >
> > > That is silly. Just make a big raid0 of it. If for some reason one ofthe
> > > 3ware cards takes a dump you WILL LOSE ALL YOUR DATA.


<yocum points over to the drbd/failsafe mailing lists>  ;-)


> >
> >(snip)
> >
> > > Which is exactly the reason to avoid the above mentioned configuration.If
> > > one card dies you have just lost all your data.
> >
> >   Personally, I'd bet on a drive or two going out before the controller.
> >I haven't had any sort of drive controller (IDE/SCSI/RAID) go out in
> >nearly a decade, but I've had plenty of drives go South on me.


This is definitely a more likely senario.  But, even in the event that we
lose 50% of our data, we're still 100% screwed, so I might as well have the
space/speed that I want/need.  If I was really paranoid, I'd be putting my
data on some fibre channel array or using drbd or something.  I'm more
interested in tons of space really, really cheap.


> 
> I have seen lots of drives go bad too. But don't discount Murphy. You might
> just have a bad day and a firmware upgrade of your controller resets the
> raid set. Most people with more then one 3ware card will set it up in JBOD
> mode and then use it as a software raid5 with a external log.
> 
> > > Which was exactly what happend. They raid
> > > controller (Ami megaraid) got upset after one disk died and they lost
> > therI
> > > complete Mysql Database.
> >
> >    Since this isn't the place, I won't point out the obvious flaws in
> >their backup/recovery scheme.
> 
> What's a backup? And recovery is for wimps ;)


File system?  Who needs a file system?  I edit inodes by hand! ;-)


> I just feel that my data would not be safe with the setup that you have
> provided. They even had bugs in the 3ware raid config which caused
> corruption in degraded mode. If that happens on your raid0 array or any
> array you are going to lose data. But I think that the chances of severe
> damage will grow in this raid0 setup.


FWIW, I got really good at reliably corrupting my data with the 3ware 6800
card and RAID5: just turn off a drive while it was writing.  Bad things
happened.  I've been testing 3 7810 cards they lent to me a couple weeks
ago, and I haven't had a problem yet (after ~10TB write/reads and ~12
simulated drive failures under a variety of high and low I/O and CPU duty
cycles.

Cheers,

Dan


-- 
Dan Yocum
Sloan Digital Sky Survey, Fermilab  630.840.6509
yocum@xxxxxxxx, http://www.sdss.org
SDSS.  Mapping the Universe.


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