Is this a reply to Paul’s message from 11 months ago?
https://bit.ly/32oZGlR
The PM1725b is interesting in that it has explicitly configurable durability vs
capacity, which may be even more effective than user-level short-stroking /
underprovisioning.
>
> Hi. How do you say 883DCT is faster than 970 EVO?
> I saw the specifications and 970 EVO has higher IOPS than 883DCT!
> Can you please tell why 970 EVO act lower than 883DCT?
The thread above explains that. Basically it’s not as simple as “faster”. IOPS
describe behavior along one axis under a certain workload for a certain length
of times. Subtle factors:
* With increasing block size, queue depth, operation rate / duration, some
less-robust drives will exhibit cliffing where their performance falls off
dramatically
——————
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(that may or may not render usefully, your UMA may vary)
Or they may lose your data when there’s a power event.
* Is IOPS what you’re really concerned with? As your OSD nodes are
increasingly saturated by parallel requests (or if you’re overly aggressive
with your PG ratio) , you may see more IOPS / throughput, at the risk of
latencying going down the drain. This may be reasonably acceptable for RGW
bucket data, but maybe not indexes and for sure not for RBD volumes.
* The nature of the workload can dramatically affect performance
** block size
** queue depth
** r/w mix
** sync
** phoon
** etc
This is one thing that (hopefully) distinguishes “enterprise” drives from
“consumer” drives. There’s one “enterprise” drive (now EOL) that turned out to
develop UREs and dramatically increased latency when presented with an actual
enterprise Ceph — vs desktop — workload. I fought that for a year and found
that older drives actually fared better than newer, though the vendor denyed an
engineering or process change. Consider the total cost of saving a few bucks
on cheap drives that appear *on paper* to have attractive marketing specs, vs
the nightmares you will face and the other things you won’t have time to work
on if you’re consumed with pandemic drive failures.
Look up the performance firmware update history of the various 840/860 EVO even
when used on desktops, which is not to say that the 970 does or doesn’t exhibit
the same or similar issues. Consider if you want to risk your
corporate/production data, applications, and users on desktop-engineered drives.
In the end, you really need to buy or borrow eval drives and measure how they
perform under both benchmarks and real workloads. And Ceph mon / OSD service
is *not* the same as any FIO or other benchmark tool load.
https://github.com/louwrentius/fio-plot
is a delightfully visual tool that shows the IOPS / BW / latency tradeoffs
Ideally one would compare FIO benchmarks across drives and also provision
multiple models on a given system, slap OSDs on them, throw your real workload
at them, and after at least a month gather drive/OSD iops/latency/bw metrics
for each and compare them. I’m not aware of a simple tool to manage this
process, though I’d love one.
ymmocv
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