[gpfsug-discuss] SSD LUN setup

[Brian Marshall]

@Jonathan,

I completely agree on the SSD failure.  I wasn't suggesting that better
write endurance made them impervious to failures, just that I read a few
articles from ~3-5 years back saying that RAID5 or RAID6 would destroy your
SSDs and have a really high probability of all SSDs failing at the same
time as the # of writes were equal on all SSDs in the RAID group.  I think
that's no longer the case and RAID6 on SSDs is fine.  I was looking for
examples of what others have done:  RAID6, using GPFS data replicas, or
some other thing I don't know about that better takes advantage of SSD
architecture.  Background - I am a storage noob

Also is the @Jonathan proper list etiquette?

Thanks everyone to great advice I've been getting.

Thank you,
Brian

On Sun, Jul 17, 2016 at 5:49 PM, Jonathan Buzzard <jonathan at buzzard.me.uk>
wrote:

> On 17/07/16 03:56, Brian Marshall wrote:
>
>> When setting up SSDs to be used as a fast tier storage pool, are people
>> still doing RAID6 LUNs?  I think write endurance is good enough now that
>> this is no longer a big concern (maybe a small concern).  I could be
>> wrong.
>>
>> I have read about other products doing RAID1 with deduplication and
>> compression to take less than the 50% capacity hit.
>>
>>
> There are plenty of ways in which an SSD can fail that does not involve
> problems with write endurance. The idea of using any disks in anything
> other than a test/dev GPFS file system that you simply don't care about if
> it goes belly up, that are not RAID or similarly protected is in my view
> fool hardy in the extreme.
>
> It would be like saying that HDD's can only fail due to surface defects on
> the platers, and then getting stung when the drive motor fails or the drive
> electronics stop working or better yet the drive electrics go puff
> literately in smoke and there is scorch marks on the PCB. Or how about a
> drive firmware issue that causes them to play dead under certain work
> loads, or drive firmware issues that just cause them to die prematurely in
> large numbers.
>
> These are all failure modes I have personally witnessed. My sample size
> for SSD's is still way to small to have seen lots of wacky failure modes,
> but I don't for one second believe that given time I won't see them.
>
> JAB.
>
> --
> Jonathan A. Buzzard                 Email: jonathan (at) buzzard.me.uk
> Fife, United Kingdom.
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