Re: L'udev, el raid1 i la mare que els va ...
Aprofondint un xic més en el problema, et copio un missatge que detalla el
problema un xic més (qüestió de timing)
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I've just had problem with this on an FC3 machine. mkinitrd-4.1.18-2.
Actually, two problems.
First was that SCSI devices are detected asynchroniously, second was
that udev seems to be working asynchroniously. Quick and dirty
workaround was adding "sleep 10" after "insmod /lib/sym53c8xx.ko"
line, and another "sleep 10" after "/sbin/udevstart" in init script
(inside initrd image).
Without the "sleep" lines, init script would simply load the modules,
and execute udevstart withoug waiting for things be initialized
properly. When raidautorun is called, the devices are not yet
detected, so it fails to initialize RAID1 device that holds physical
volume (under LVM) with root partition on it.
I've asked about this on Linux kernel mailing list (LKML). I got
answer that this should be delt within init script that is generated
by mkinitrd. In short, PCI is hot-pluggable, and everything on it is
asynchronious. When driver loads, it starts asynchroniously searching
for devices, which sometimes can take long time. Making assumption
that things are synchronious (as mkinitrd seems to be making) is
simply wrong. It takes about 5 seconds for sym53c8xx driver to detect
disk devices on my dual SCSI card (integragted into motherboard) after
it is loaded. One person replied that FreeBSD is waiting 15 seconds
for SCSI buses to initialize. Linux dosn't waste time waiting, nor
init script does.
I guess with most devices and drivers this race condition that exists
in mkinitrd generated init script won't be hit (drivers are fast
enough in detecting the hardware). But the race condition exists, and
can be a problem on certain hardware configurations.
The fix made in 4.1.4 dosn't seem to affect this case. The problem
here is not non-existing device node, the problem is that SCSI driver
is slow in detecting disks. Should this bug be reopened?
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El que ja no sé és si usant un kernel personalitzat, sense initrd i amb
els drivers compilats estàticament, això també passaria. Qüestió de
provar-ho.
Ah! una altre detall. No sé si saps que el directori /dev antic segueix
tenint la seva existència (tot i que miserable i condemnada a l'extinció)
com a directori ocult a /.dev
Una tercera opció seria crear els dispositius a /.dev, i almenys no
s'esborren cada vegada que arrenques. Llavors s'ha de modificar el fitxer
de configuració del raid per tal que vagi a cercar a /.dev enlloc de /dev
Apa, bona setmana santa.
Orestes.
> Acabo de donar una ullada als reports dels RCB i veig que efectivament no
> acaben de posar-se d'acord alhora d'assignar-ho i de moment sembla que la
> glòria se l'emporta el mdadm i un tal Samuel diu que a ell li ha funcionat
> canviat la prioritat de manera que arrenqui l'mdadm abans de l'udev ...
>
> De moment ja tinc dues solucions que ja està bé :)
>
> Gràcies !!!
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