Re: [9fans] "FAWN: Fast array of wimpy nodes" (was: Plan 9 - the next 20 years)

[erik quanstrom <quanstro@coraid.com>]

On Mon Apr 20 11:13:01 EDT 2009, jbarham@gmail.com wrote:
> > could you explain how raid 5 relates to sata vs sas?
> > i can't see now it's anything but a non-sequitor.
>
> Here is the motivating real-world business case: You are in the movie
> post-production business and need > 50 TB of online storage at as low
> a price as possible with good performance and reliability.  7200 rpm
> SATA (currently ~15¢/GB on Newegg)

this example has nothing to do with raid.  if the object is to find the
lowest cost per gigabyte, enterprise sata drives are the cheeper option.
(it would make more sense to compare 7.2k sas and sata drives.  there
is also a premium on spindle speed.)

the original argument was that scsi is better than ata or sas is better
than sata (i'm not sure which); in my opinion, there are no facts
to justify either assertion.

> plus RAID narrows the performance
> and reliability of benefits of 15k rpm SAS (currently ~$1/GB) at a
> much lower cost.

without raid, such a configuration might be impossible to deal with.

most 15k drives are 73gb.  this means you would need 685 for 50tb.
the afr is probablly something like 0.15% - 0.25%.  this would mean you
will loose 1-2 drives/year.  (if you believe those rosy afr numbers.)

- erik