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Bug#838503: debian-installer: mdadm should not start syncing RAID1 arrays at full speed during installation



Hi Baptiste,

Baptiste Jonglez <debian@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…

> 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.


KiBi.

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