[Beowulf] how cluster's storage can be flexible/expandable?

Vincent Diepeveen diep at xs4all.nl
Tue Nov 13 12:40:12 PST 2012

On Nov 13, 2012, at 9:17 PM, Greg Keller wrote:

> From: Joe Landman <landman at scalableinformatics.com>  That's not the  
> issue with glusterfs.  It's distributed metadata architecture is a  
> double edged sword.  Very good for distributed data, very very bad  
> for metadata heavy ops.
> That and the xfs attributes haven't been slow in years though some  
> folks like bringing up the old behavior pre 2.6.26 as examples of  
> why you shouldn't use it.   Dave Chinner has a great presentation  
> on the topic from 15 months ago or so.  Puts down real numbers.   
> Situation is rather different than implied.
> We've recently seen XFS kill a pretty important server after an  
> abrupt power off.  It appears someone decided they needed to force  
> it to be "POSIX" compliant by default, and as a result XFS doesn't  
> sync/flush to disk unless told to or some rather long timeout (30  
> seconds can be verrry long ).

You sure this is just XFS problem?

Linux also has this behaviour towards floppy disk over here and that  
floppy disk doesn't have XFS.

Maybe it's a kernel feature that assumes most people have a cheap WD  

In fact to save the new generation harddisks from for example WD that  
could be interesting feature.

I've read some reports that the cheap versions of them quite quickly  
go to power savings mode, though not sure how long it takes
to reach that idle mode. Then it would spin up again when there is  
disk activity. Yet this flip between power saving and spinning active
if i see some users report it, that can be done only a limited amount  
of time, which would normally spoken give the disk because of
that an average lifetime of no more than a year or so in case your  
machine is writing regurarly something to disk.

Maybe this feature of XFS helps a tad there? Or should it wait for 30  
minutes then to write to disk?

> Has anyone else seen this / been surprised / re-tuned / written the  
> how-to for me?
> If you tune it you can get it back to it's good old days...  
> flushing routinely.... but we haven't messed with it much since.   
> XFS, RIP...  at least for until we need it again :)
> GlusterFS... my jury is still out.  I tried it once with some  
> viscous metadata munging code and Joe told me never to do that to  
> Gluster again I think.  The code was abusive honestly, nearly evil.
> Cheers!
> Greg
> "Joe Landman, now there's a frood who knows where his towel is!"
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