Hi Colin, I sent this yesterday but not sure it was processed:
OK so after spending many more hours, I found that 10 disk RAID 6 members are bootable (mdadm assembles in grub) while 11 disk and above does not. This is from very simple VMWare test using the latest Jessie ISO build, and a clean install. Once you hit 11 members in RAID 6, grub drops to rescue complaining it can't find the uuid. This aligns with the 8-disk limit. In RAID 6, you will need 8 usable disks to assemble a 10-disk member array (two parity). So grub can see only the first 8 disks, which is enough to get us started. So I believe there is still an 8-disk limit in grub and this is a bug. As for the VMWare setup, I created (14) HDD's @ 10GB in size each and assigned them to an LSI Logic SAS bus controller. Installed Debian, assigned each 14 disk to RAID, then tried various mdadm configurations randing from 8 disks to 14 disks to determine that grub is stopping at the 8 disk limit with mdadm. I also tried RAID 0 to make sure it wasn't a RAID 6 issue and had the same result. I am happy to post my entire VMWare file if you want (~2GB). I'll email you the link. Regarding previous versions of grub, I know only that the stable 1.99 has the same problem because I upgraded to 2.x in an effort to fix it. -----Original Message----- From: Colin Watson [mailto:[email protected]] Sent: Sunday, October 12, 2014 2:36 AM To: Mike B; [email protected] Subject: Re: Bug#764798: grub2: Grub rescue shell with RAID 6 mdadm over 8 disks On Sat, Oct 11, 2014 at 03:00:11AM -0500, Mike B wrote: > Package: grub2-common > Version: 2.02~beta2-11 > Severity: critical > File: grub2 > Justification: breaks the whole system Do you know if there was a previous version of GRUB 2 where this worked? For example, how does the version in testing behave? (This is for practical reasons: if this has just always been broken in GRUB 2, then it shouldn't block migration of 2.02~beta2 to testing.) > I initially was running an 8-disk RAID 6 mdadm. Everything worked > fine. The system was upgraded to 14 disks RAID 6 online. Eventually > the system was rebooted and now grub drops to rescue complaining of > invalid UUID. > > Upon further inspection, grub is only seeing 8 disks (ls) instead of > 14 and cannot assemble the root mdadm device. OK, so that implies that this doesn't have much directly to do with RAID handling: the problem is probably simply that GRUB can't see all 14 disks. > I've tested using VMWare and confirmed that 8-disk RAID 6 mdadm arrays > work fine with grub for root, but 9 disk and above break the system > and drop to rescue shell. A quick test in qemu shows that GRUB can see more than eight disks there. Could you please share details of your VMware setup so that I might stand a chance of reproducing this? Thanks, -- Colin Watson [[email protected]] -- To UNSUBSCRIBE, email to [email protected] with a subject of "unsubscribe". Trouble? Contact [email protected]
