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From Terje Marthinussen <>
Subject Re: raid 0 and ssd
Date Thu, 14 Apr 2011 07:01:33 GMT

You should notice that unless you have TRIM, which I don't think any OS
support with any raid functionality yet, then once you have written once to
the whole SSD, it is always full!

That is, when you delete a file, you don't "clear" the blocks on the SSD so
as far as the SSD goes, the data is still there.

The latest SSDs are pretty good at dealing with this though, and some can be
made a lot better by allocating extra spare block area for GC.

Also be careful with raids and things like scrubbing or initialization of
the Raid. This may very well "fill it 100%" :)


On Thu, Apr 14, 2011 at 2:02 PM, Drew Kutcharian <> wrote:

> RAID 0 is the fastest, but you'll lose the whole array if you lose a drive.
> One thing to keep in mind is that SSDs get slower as they get filled up and
> closer to their capacity due to garbage collection.
> If you want more info on how SSDs perform in general, Percona guys have
> done extensive tests. (In addition to comparing all the raid levels and etc.
> the "RELATED
SEARCHES" on the right side too)
> - Drew
> On Apr 13, 2011, at 9:42 PM, Anurag Gujral wrote:
> > Hi All,
> >            We are using three ssd disks with cassandra 0.7.3 , should we
> set them as raid0 .What are the advantages and disadvantages of doing this.
> > Please advise.
> >
> > Thanks
> > Anurag

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