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SubjectRe: [ANNOUNCE] RAIF: Redundant Array of Independent Filesystems
> 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

> > 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.

Nikolai Joukov, Ph.D.
Filesystems and Storage Laboratory
Stony Brook University
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