"I forgot to run LILO" [LWN.net]

"I forgot to run LILO"

Posted Dec 13, 2010 13:10 UTC (Mon) by etienne (subscriber, #25256)
In reply to: "I forgot to run LILO" by dlang
Parent article: Getting grubby with ZFS

I would say, it depends what you call lots of drives.
Things like 4 to 8 drives (whatever their BIOS numbers, i.e. IDE or USB) would be treated without problems.
The compiled-in limit are 10 IDE interfaces, 15 disks, 64 partitions per disks (including extended partitions, i.e. 34 useable).
The real limit is that the number of "ways to boot", i.e. kernels and DOS/windows MBRs should be lower than 60, but it is true that if you want to analyse the max number of filesystems to search for all possible kernels and initrd, it will start slowly.

There is for instance no problem having Fedora, Ubuntu and debian distributions in both 32 and 64 bits installed on the same PC (i.e. 6 distributions in 6+ different partitions), plus kind of 10-20 iso images of live CD distributions.
One problem with other bootloaders is that when you boot from a USB key, some PC shift all BIOS drives numbers, so that number cannot be safely written in a static configuration file.

For instance, if you have a distribution on a USB disk, distribution containing it own /boot/gujin.cmd to supply its own command line to its own kernel, you can boot your PC with or without this disk connected; Gujin will automatically recognise that way to boot and display a line in the menu.
It doesn't matter if Gujin came from the hard disks or the USB disk.

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"I forgot to run LILO"

Posted Dec 15, 2010 4:44 UTC (Wed) by dlang (✭ supporter ✭, #313) [Link]

my home server has 3 SCSI drives,2 SATA drives, and 12 IDE drives, at work I've had single systems with up to 46 drives visible to the OS (16-18 drives is fairly common in a 3u chassis)

your description of the many-OS system can still be done with very few drives

"I forgot to run LILO"

Posted Dec 15, 2010 10:39 UTC (Wed) by etienne (subscriber, #25256) [Link]

> my home server has ...

Well, the 15 disks limit was done because it is said that some BIOS would have a problem - and BIOS disk 0x90 was the same as BIOS disk 0x80...
But as long as your vmlinuz/initrd pair is located in one of the first 15 disks Gujin should still work.
Moreover, I assume that you start your system with some disk in "power on standby mode" - or else you have a massive power supply; those disks will not contain the /boot partition.
Gujin has been tested with disks in "power on standby mode".
With such a system, if your main MBR is corrupted and you try to boot from a USB key, and that key is mapped by the BIOS as disk 0x80 (shifting all other disks numbers by one), your preconfigured mapping in either Grub or LILO will be wrong (trying to load from the wrong disk).
Increasing the default number of disk supported in Gujin is a single "#define NB_DISK" change, maybe I'll increase the default.

> your description of the many-OS system can still be done with very few drives

One drive is enough, but the complexity to manage the six Grub configurations in six partitions is a nightmare...

"I forgot to run LILO"

Posted Dec 15, 2010 19:53 UTC (Wed) by dlang (✭ supporter ✭, #313) [Link]

actually no, my boot disk is one of the SCSI drives, which the system puts out at drive /dev/sdo (or thereabouts).

the IDE drives are connected to 3-ware raid cards (but not using the raid features of the cards), not directly to the motherboard.

"I forgot to run LILO"

Posted Dec 20, 2010 13:58 UTC (Mon) by nix (subscriber, #2304) [Link]

Most controllers which permit the attachment of >3 disks also have a mode (often the default), whereby the controller powers up the drives in sequence, not simultaneously (but still powers them all up in POST, rather than having some strange mode where it powers only some of them up until receiving a request from software to power up the rest).