FW: 20TB Storage System

[Max Clark]

I know adding ccd/vinum to the equation will lower my IO throughput, but the
question is... if I have an external hardware shelf with 3.5TB (16 250GB
drives w/ Raid 5 from hardware) and I put a Raid 0 stripe across 3 of these
shelves what would my expected loss of IO be?

Thanks,
Max

-----Original Message-----
From: Poul-Henning Kamp [mailto:phk at phk.freebsd.dk]
Sent: Tuesday, September 02, 2003 1:02 PM
To: Max Clark
Cc: freebsd-questions at freebsd.org; freebsd-performance at freebsd.org;
freebsd-hackers at freebsd.org
Subject: Re: FW: 20TB Storage System


In message <ILENIMHFIPIBHJLCDEHKIEMEDCAA.max.clark at media.net>, "Max Clark"
writ
es:

>Given the above:
>1) What would my expected IO be using vinum to stripe the storage
enclosures
>detailed above?

That depends a lot on the applications I/O pattern, an I doubt a
precise prediction is possible.

In particular the FibreChannel is hard to predict the throughput off
because the various implementations seems to have each their own
peculiar quirks performance wise.

On a SEAGATE ST318452 disks, I see sequential transfer rates
at the outside rim of the disk of 58MB/sec.  If I stripe two of
them them with CCD I get 107MB/sec.

CCD has a better performance than Vinum where they compare.

RAID-5 and striping a large number of disks does not scale linearly
performance wise, in particular you _may_ see your average access
time drop somewhat, but there is by far no guarantee that it will
be better than the individual drive.

>2) What is the maximum size of a filesystem that I can present to the host
>OS using vinum/ccd? Am I limited anywhere that I am not aware of?

Good question, I'm not sure we currently know the exact barrier.

>3) Could I put all 20TB on one system, or will I need two to sustain the IO
>required?

Spreading it will give you more I/O bandwidth.

--
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.