Skip to main content

Booting multipathed Linux using GRUB

As a side-effect of the Linux boot process, I suddenly realized that our boot process is not fault-tolerant! We have 100+ servers that boot from SAN using two Qlogic 2460 HBAs. We installed EMC PowerPath 5.0.0 on OEL 4u5 to get multipathing and automatic fail-over in case a path fails. The OS is pretty well off in case of hardware faults.
However, the boot process is not! Not even close! In stage 1, the boot loader reads the MBR, loads stage 1.5 so it can read the /boot ext2 partition where the kernel and initrd image are located. In our case, this is /dev/sdb1. But what if my HBA dies and /dev/sdb1 doesn't exist? It may be smart enough to try a device using the other path, but probably not. Also, since the kernel hasn't loaded yet, PowerPath does not exist and there is no multipath awareness to save the day...

So once systems are installed and the number of disk partitions is stable, I can
enhance GRUB with boot fallback systems, so it will try /dev/sdb1 and it that fails switch to /dev/sdm1 (actual device name dependent on the number of disks (LUNs) that system has.
Labels:

Comments

Post a Comment

Popular posts from this blog

Preventing PuTTY timeouts

Just found a great tip to prevent timeouts of PuTTY sessions. I'm fine with timeouts by the host, but in our case the firewall kills sessions after 30 minutes of inactivity... When using PuTTY to ssh to your Linux/Unix servers, be sure to use the feature to send NULL packets to prevent a timeout. I've set it to once every 900 seconds, i.e. 15 minutes... See screenshot on the right.
1 comment
Read more

Removing VGs or LVs from LVM

While are many excellent tutorials about creating and using LVM on Linux, not may show you how you can remove disks from LVM Volume Groups (VG) and reclaim storage or how to remove a Logical Volume (LV) from your LVM set-up. Here is what I did: Use -t to TEST ANY LVM action first! We are going to release 1 TB from LVM. The Volume group was extended with 1 TB storage to serve as a cheap NFS/CIFS file server when setting up our data center. It is now deprecated and replaced by a NAS so it's no longer needed. 1) check LVM; note the four 256 GB LUNs [root@server ~]# pvscan -v Wiping cache of LVM-capable devices Wiping internal VG cache Walking through all physical volumes PV /dev/sdb1 VG vgdata lvm2 [50.00 GB / 0 free] PV /dev/sdc1 VG vgdata lvm2 [256.00 GB / 0 free] PV /dev/sdd1 VG vgdata lvm2 [256.00 GB / 0 free] PV /dev/sde1 VG vgdata lvm2 [256.00 GB / 0 free] PV /dev/sdf1 VG vgdata lvm2 [256.00 GB / 0 free] PV /dev/sdg ...
Post a Comment
Read more

Tuning the nscd name cache daemon

I've been playing a bit with the nscd now and want to share some tips related to tuning the nscd.conf file. To see how the DNS cache is doing, use nscd -g. nscd configuration: 0 server debug level 26m 57s server runtime 5 current number of threads 32 maximum number of threads 0 number of times clients had to wait yes paranoia mode enabled 3600 restart internal passwd cache: no cache is enabled [other zero output removed] group cache: no cache is enabled [other zero output removed] hosts cache: yes cache is enabled yes cache is persistent yes cache is shared 211 suggested size 216064 total data pool size 1144 used data pool size 3600 seconds time to live for positive entries 20 seconds time to live for negative entries 66254 cache hi...
2 comments
Read more