On Fri, Nov 20, 2009 at 2:42 PM, Bill McGonigle <[email protected]> wrote: >> Software-based solutions -- which don't kick in >> until the OS is running -- sometimes get caught up trying to boot from >> a failed disk. > > "Please don't use RAID-5". >A healthy, properly configured (and tested) RAID-1 will boot nicely.
It's not an issue with RAID 1 vs 5. The issue is that non-RAID cards are not intelligent. Here's the scenario: System powers on. Disks spin up, servo heads, come online. BIOS sees both disks as reporting online. BIOS reads the MBR from disk 0, finds a valid signature, tries to boot from it. The bootstrap in the MBR proceeds to try and load additional stages. One of those includes a bad block. Loader aborts with an I/O error. System sits there like a dumb shit forever. Disk 1 is fine and would work, but the BIOS doesn't know that. An alternate scenario is the system just hangs or aborts trying to read the MBR from disk 0. Optionally, have a watchdog that reboots the system. System sits in a boot loop forever. If this hasn't happened to you yet, lucky you. I sincerely hope your luck continues. My luck is not as good as yours. With a hardware RAID controller, the first time disk 0 has a bad block, the controller will fail that disk out of the RAID set, and use disk 1 for everything. The BIOS is never even aware there is a problem. The disks are behaving; I don't want disk drives to self-destruct and report "Not Ready" (and thus be totally unusable) just because they have non-zero bad blocks. You could argue that the alternate scenario above is the fault of the BIOS or disk controller, that it should be able to recover from an I/O error on disk 0 and move on and try disk 1. You're prolly right. But this is the pee sea platform we're talking about here. I don't really need to explain the environment to you, do I? ;-) And the BIOS is still helpless once the MBR bootstrap takes over. -- Ben _______________________________________________ gnhlug-discuss mailing list [email protected] http://mail.gnhlug.org/mailman/listinfo/gnhlug-discuss/
