Re: [ANNOUNCE] RAIF: Redundant Array of Independent Filesystems

[Al Boldi <a1426z@gawab.com>]

Nikolai Joukov wrote:
> > Nikolai Joukov wrote:
> > > We have designed a new stackable file system that we called RAIF:
> > > Redundant Array of Independent Filesystems.
> >
> > Great!
> >
> > > We have performed some benchmarking on a 3GHz PC with 2GB of RAM and
> > > U320 SCSI disks.  Compared to the Linux RAID driver, RAIF has
> > > overheads of about 20-25% under the Postmark v1.5 benchmark in case of
> > > striping and replication.  In case of RAID4 and RAID5-like
> > > configurations, RAIF performed about two times *better* than software
> > > RAID and even better than an Adaptec 2120S RAID5 controller.
> >
> > I am not surprised.  RAID 4/5/6 performance is highly sensitive to the
> > underlying hw, and thus needs a fair amount of fine tuning.
>
> Nevertheless, performance is not the biggest advantage of RAIF.  For
> read-biased workloads RAID is always slightly faster than RAIF.  The
> biggest advantages of RAIF are flexible configurations (e.g., can combine
> NFS and local file systems), per-file-type storage policies, and the fact
> that files are stored as files on the lower file systems (which is
> convenient).

Ok, a I was just about to inform you of a three nfs-branch raif which was 
unable to fill the net pipe.  So it looks like a 25% performance hit across 
the board.  Should be possible to reduce to sub 3% though once RAIF matures, 
don't you think?


> > > This is because RAIF is located above
> > > file system caches and can cache parity as normal data when needed. 
> > > We have more performance details in a technical report, if anyone is
> > > interested.
> >
> > Definitely interested.  Can you give a link?
>
> The main focus of the paper is on a general OS profiling method and not
> on RAIF.  However, it has some details about the RAIF benchmarking with
> Postmark in Chapter 9:
>
>   <http://www.fsl.cs.sunysb.edu/docs/joukov-phdthesis/thesis.pdf>
>
> Figures 9.7 and 9.8 also show profiles of the Linux RAID5 and RAIF5
> operation under the same Postmark workload.


Thanks!

--
Al