Re: [9fans] just an idea (Splashtop like)

[erik quanstrom <quanstro@coraid.com>]

> Ron, have you researched any long-term wear studies on these flash
> drives? I've heard a lot of good things,
> but I'm really put off by terms like "wear levelling", filesystems
> optimized to work around flash's delicateness,
> etc.
>
> I'm really interested in any numbers anyone has.

just looking at the intel x25-e datasheet, the URE rate
(unrecoverable read error) is the same as enterprise sata
drives at 1e-15, but the mtbf is higher, but within a factor
of two.

assuming honest mtbf numbers, one would expect similar
ures for the same io workload on the same size data set
as mechanical disks.  since flash drives are much smaller,
there would obviously be fewer ures per drive.  but needing
10x more drives, the mtbf would be worse per byte of storage
than enterprise sata drives.  so you'd see more overall failures.

conclusion: you'll need raid for flash drives, too.

this is a pretty suprising result.  and i'm sure that a large
number of people are going to jump up and argue.  but
here are the datasheets.

http://download.intel.com/design/flash/nand/extreme/319984.pdf
http://www.wdc.com/en/library/spec/2879-701281.pdf
(i didn't see the wdc mtbf but i've seen it quoted as 1.2Mhrs, as
http://hothardware.com/News/WD-Introduces-RE3-Enterprise-SATA-Hard-Drives/
)

perhaps the reason that it's so suprising is the same reason
we didn't pay attention to the ure rate when hard drives were
512mb.  would you expect to have a bad spot in 2,000 fujitsu
eagles?  that's ~ the amount of data you can store on one tb drive.

- erik