Re: IO scheduler recommendation

On 28/01/2019 14.15, Imre Samu wrote:
> Phoronix website has some performance testing.
>
> for example:  (2018 Dec)  "Linux 4.20 I/O Scheduler Benchmarks On NVMe
> SSD Storage"
> https://www.phoronix.com/scan.php?page=article&item=linux-420-io&num=3
> "BFQ also picked up wins on the Samsung 970 EVO SSD when running the
> PostgreSQL database server."
>
> (2017)"Linux 4.12 I/O Scheduler Benchmarks: BFQ, Kyber, Etc"
> https://www.phoronix.com/scan.php?page=article&item=linux-412-io&num=3
> "The default CFQ I/O scheduler on this SATA 3.0 SSD system remained
> the fastest for this PostgreSQL benchmark."
>
> Imre
>
>
> AB_ba# <bharti(dot)anup(at)gmail(dot)com <mailto:bharti(dot)anup(at)gmail(dot)com>> ezt írta
> (időpont: 2019. jan. 21., H, 12:05):
>
> Hello ,
>
> I searched the complete PostgreSQL Documentation but didn't get
> anything with respect to IO scheduler recommendation.
> What is being recommended by PostgreSQL ?
> Which is the best IO scheduler considering the Data is hosted on NFS?
>
>
> --
> Thanks and Regards
> ANUP BHARTI
>

CFQ is supposed to be the best for servers anyway, because it is
designed to ensure all services get fair (hence the name) amount of I/O
transfer time, no matter what. Deadline is supposed to be better for
interactive (e.g. desktop) use because it guarantees better response at
the expense of overall throughput.

The above mentioned schedulers are variants of the Elevator algorithm
designed to optimize data handling on a rotating platter HDD with moving
heads. NOOP scheduler, as its name sugests, does nothing. It is supposed
to be best for devices which are NOT rotating platter, moving heads
HDDs. Its case uses are SSDs which don't have mechanical movements to
optimize, RAID controllers which themselves control their physical
drives and VMs where the host OS is responsible for that.

However all that is moot for NFS, which is used by the OP, for it is a
network protocol, not a physical device. The question of schedulers is
irrelevant because it CAN'T be set for NFS.

--
Kind Regards,
Arni Kromić