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SubjectRe: [ANNOUNCE] RAIF: Redundant Array of Independent Filesystems
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:
> <>
> Figures 9.7 and 9.8 also show profiles of the Linux RAID5 and RAIF5
> operation under the same Postmark workload.



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