On Thu, Dec 06, 2018 at 11:09:01PM +0000, Steve McIntyre wrote: >[ Responding to this old bug, prompted by discussion in #debian-boot > tonight ] > >On Sat, Jun 24, 2017 at 09:01:49PM +0200, Cyril Brulebois wrote: >>Hi Baptiste, >> >>Baptiste Jonglez <deb...@bitsofnetworks.org> (2016-09-21): >>> When creating a RAID1 array in the debian-installer and using it for >>> the installation, mdadm immediately starts syncing the disks of the >>> RAID array. >>> >>> This is a bad idea, because the subsequent install will be really slow >>> on rotational disks (linear disk access by mdadm and random disk >>> access by dpkg). On a fairly recent computer with 2 SATA disks, the >>> installation took around 20 minutes before even arriving to the >>> tasksel step. >> >>Well, I can understand the argument, but the user could very well expect >>disks to be in mirror mode as soon as possible, and not wait until a few >>days after the installation before the initial sync ends… > >The number isn't persistent across reboots, so it would speed up again >on the reboot after the installation finished. > >>> I can see two solutions: >>> >>> 1) lower the speed of the syncing operation, by setting the >>> "dev.raid.speed_limit_max" sysctl setting to e.g. 1000; >> >>I'm not sure it would be a good idea to stick a hardcoded value there, >>even if we were to lower the available bandwidth… Too many different >>cases, be it about actual hardware, disk sizes, etc. > >1000 is a nice small number, which I think might make sense as a >default *while* we're installing. Once the installer has finished and >the system is rebooted, all will go back to normal. Hell, we could >even expose this value via debconf for expert (and preseed) if needed.
So, I've been playing with this some more. For people who care deeply about this now: * if you're preseeding your setup, add the following to control RAID resync speed d-i partman/early_command \ string modprobe md_mod; echo 2000 > /proc/sys/dev/raid/speed_limit_max (this will limit resync speeds to a max of 2000 K/sec) * if you're running d-i by hand, switch to another console then: # echo <SPEED> > /sys/block/<MD>/md/sync_speed_max after you've created your RAID devices -- Steve McIntyre, Cambridge, UK. st...@einval.com Dance like no one's watching. Encrypt like everyone is. - @torproject