On 04/07/2014 03:38 PM, Lux, Jim (337C) wrote:
On 4/7/14 12:11 PM, "Lockwood, Glenn" <[email protected]> wrote:
On Apr 7, 2014, at 11:53 AM, Prentice Bisbal
<[email protected]> wrote:
4. SSDs wearing out. Is that still a concern, or are lifespans getting
better?I think Jim Lux once did calculations on that list to show that
with wear-leveling and everything else, even if you wrote to an SSD
constantly, it would still outlive the average lifespan of a cluster.
As long as you use enterprise-grade SSDs (e.g., Intel's stuff) with
overprovisioning, the nand endurance shouldn't be an issue over the
lifetime of a cluster. We've used SSDs as our nodes' system disks for a
few years now (going on four with our oldest, 324-node production
system), and there have been no major problems. The major problems
happened when we were using the cheaper commodity SSDs. Don't give in to
the temptation to save a few pennies there.
Was it wear out, or some other failure mode?
And if wear out, was it because consumer SSDs have lame leveling or
something like that?
Here's how I remember it. You took the capacity of the disk, figured out
how much data would have to be written to it wear it out, and then
divided that by the bandwidth of the drive to figure out how long it
would take to write that much data to the disk if data was constantly
being written to it. I think the answer was on the order of 5-10 years,
which is a bit more than the expected lifespan of a cluster, making it a
non-issue.
That's how I remember it, how it actually happened could be different. I
could try search the archives, but if there's one thing I've learned
from CNN, it's that speculation is better than actual facts.
--
Prentice Bisbal
Manager of Information Technology
Rutgers Discovery Informatics Institute (RDI2)
Rutgers University
http://rdi2.rutgers.edu
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