PMP support build-in or recompile?

cert · April 10, 2016

Hi!

Is PMP support build-in in newer armbian images? I installed ARMBIAN Debian GNU/Linux 8 (jessie) 4.4.3-sunxi on my banana pi. Or is a recompile still needed? With the default image i can see a dmesg "error ahci-sunxi 1c18000.sata: controller can't do PMP, turning off CAP_PMP".

If recompile is needed can someone please post a link where to find step-by-step instructions how to recompile armbian with PMP support? Is the guide on htpcguides.com still correct?

Thank you

tkaiser · April 10, 2016

Playing PMP with A20 is always crap, especially when misused together with RAID: http://linux-sunxi.org/SATA#Caveats

To enable PMP capabilities, you need to use our build system and rename port_multiplier.patch.disabled to port_multiplier.patch and then you either compile as a module to be able to use PMP or not by starting the module differently or if you want the rootfs on a disk behind the port multiplier (really insane stuff), you have to say "Y" at compile time:

TL;DR: Do not use port multipliers with A20. It's crap. Cheap port multipliers can also easily corrupt data under load.

zador.blood.stained · April 10, 2016

To enable PMP capabilities, you need to use our build system and rename port_multiplier.patch.disabled to port_multiplier.patch

This patch is for legacy kernel, but @cert wrote about image with 4.4.3 kernel.

AFAIK to enable PMP you have to add

ahci_sunxi.enable_pmp=1

to kernel argument list (boot.cmd and recompile it to boot.scr).

TL;DR: Do not use port multipliers with A20. It's crap. Cheap port multipliers can also easily corrupt data under load.

For production environment or anywhere else where data integrity is critical - yes. Also since SATA bandwidth on A20 is limtied to start with, unless you are playing with slow HDDs you may not get big speed improvement (especially for write speed).

tkaiser · April 10, 2016

you may not get big speed improvement (especially for write speed).

Thx for correcting me regarding vanilla kernel

'Speed improvement' with port multipliers? Not possible since the bottleneck is A20's SATA implementation and a port multiplier slows down a bit (there are two PM modes defined and A20 only knows the slow one so especially acessing more than one disk in parallel will slow small access patterns down).

Performance increase would only be possible by using both SATA and USB and then building a RAID-0. But most people want to use PM only to create a redundant RAID array (and then forget about backup and end up with all their data lost when one disk is failing since shortly after the crappy PM will also fail). I outlined over a year ago how I would use 2 A20 devices to provide both improved performance and reliability: http://forum.lemaker.org/forum.php?mod=redirect&goto=findpost&ptid=11857&pid=71617&fromuid=33332

zador.blood.stained · April 10, 2016

'Speed improvement' with port multipliers? Not possible since the bottleneck is A20's SATA implementation and a port multiplier slows down a bit (there are two PM modes defined and A20 only knows the slow one so especially acessing more than one disk in parallel will slow small access patterns down).

A20 SATA read speed limit is probably greater than sequential read speed for 5400rpm HDDs. But if somebody is building something out of A20 board, port multiplier and 5400rpm HDDs, I have some bad news anyway

cert · April 11, 2016

Thank you for the replies. I changed boot.scr and now dmesg shows:

[3.537379] ahci-sunxi 1c18000.sata: SSS flag set, parallel bus scan disabled
[3.537423] ahci-sunxi 1c18000.sata: AHCI 0001.0100 32 slots 1 ports 3 Gbps 0x1 impl platform mode
[3.537440] ahci-sunxi 1c18000.sata: flags: ncq sntf stag pm led clo only pmp pio slum part ccc

I connected a small SSD and a blu ray drive but nothing show up on dmesg and lsblk I just want to use the banana pi as a simple NAS without RAID. i will try to mount a small 10mmx10mm heatsink to the PMP chip.

A20 SATA read speed limit is probably greater than sequential read speed for 5400rpm HDDs. But if somebody is building something out of A20 board, port multiplier and 5400rpm HDDs, I have some bad news anyway

Whats the bad news?

EDIT: Ok connected 2 HDDs and they are listed. But SSD and blu ray not working.

Edited April 11, 2016 by cert