Re: Bonnie++ run with RAID-1 on a single SSD (2.6.29-rc4-224-g4b6136c)

[Chris Samuel <chris@csamuel.org>]

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On Saturday 14 February 2009, Chris Mason wrote:

> On Fri, 2009-02-13 at 23:31 +1100, Chris Samuel wrote:

[Bonnie++]
> > This is on a Dell E4200 with Core 2 Duo U9300 (1.2GHz), 2GB RAM
> > and a Samsung SSD (128GB Thin uSATA SSD).
>
> Thanks for posting these, it is especially good to see the metadata ops
> are still fast on this ssd.

Not a problem - sorry for the delay in responding.. :-(

> So, btrfs is doing ~28MB/s writes while writing the data  twice and XFS
> is doing 62MB writing it once.  That's not too bad really.

Yup, I'm very happy!

> But, one important thing about the ssds is they stripe internally across
> a bunch of flash storage, and then they have the FTL managing all the
> writes.

Ah...

> So, if you make two partitions on a single device, a raid1 data write
> from btrfs is very likely to result in two large IOs, which the FTL very
> well might put directly adjacent to each other on the SSD.

...yes, I can see that could well happen.  Bugger.. :-(

> Duplicating the data does make it more likely you'll recover something
> if the device goes bad, but two devices are still safer than one.

Yeah, but pretty hard to do in a very light laptop!

> I'm not saying the test isn't valid, I just want to make sure people
> reading the list don't run off and partition their ssds in hopes of
> getting raid ;)

Agreed - I'm just hoping to be a bit safer than not having it.. ;-)

cheers,
Chris
-- 
 Chris Samuel  :  http://www.csamuel.org/  :  Melbourne, VIC

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