[Beowulf] how cluster's storage can be flexible/expandable?
diep at xs4all.nl
Tue Nov 13 13:44:42 PST 2012
On Nov 13, 2012, at 9:55 PM, Greg Keller wrote:
> On Tue, Nov 13, 2012 at 2:40 PM, Vincent Diepeveen <diep at xs4all.nl>
> 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 disk?
> 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?
> No, I was told this was a conscious decision to follow the POSIX
> spec exactly. Maybe it helps not spin up drives and saves $0.07
> cents per year... but I think that's collateral savings.
> To Mr. Becker's Point, we used XFS for large filesystems for years
> with absolutely no trouble, on 100's of TB of storage. It was
> years ahead of EXT4 in making big volumes simple too EXT# types.
> Whatever was changed recently (not sure when), I would use XFS, but
> only once I really understood the tuning/flushing and did some
> sudden power off and kernel crash testing. If you're running a
> version from before the change it will probably work just like you
> think it should.
Heh Greg - didn't ext2 sync every 30 seconds as well?
So if they changed it for XFS as well i guess some old school guy
hacked a tad around in the code - this is the problem of all
companies with performance code - too many dudes who aren't thinking.
One of them can mess up for entire team.
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