Re: Write lifetime hints for NVMe

On 01/27/2018 08:06 PM, Dmitry Dolgov wrote:
>> On 27 January 2018 at 16:03, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> wrote:
>>
>> Aren't those numbers far lower that you'd expect from NVMe storage? I do
>> have a NVMe drive (Intel 750) in my machine, and I can do thousands of
>> transactions on it with two clients. Seems a bit suspicious.
>
> Maybe an NVMe storage can provide much higher numbers in general, but there are
> resource limitations from AWS itself. I was using c5.large, which is the
> smallest possible instance of type c5, so maybe that can explain absolute
> numbers - but anyway I can recheck, just in case if I missed something.
>

According to [1] the C5 instances don't have actual NVMe devices (say,
storage in PCIe slot or connected using M.2) but EBS volumes exposed as
NVMe devices. That would certainly make explain the low IOPS numbers, as
EBS has built-in throttling. I don't know how much of the NVMe features
does this EBS variant support.

Amazon actually does provide instance types (f1 and i3) with real NVMe
devices. That's what I'd be testing.

I can do some testing on my system with NVMe storage, to see if there
really is any change thanks to the patch.

[1]
https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/nvme-ebs-volumes.html

--
Tomas Vondra http://www.2ndQuadrant.com
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