Fajar Priyanto wrote: > On Thursday 09 March 2006 05:07 pm, Simone wrote: > >> Hi, once you remove sda, you need to setup grub on sdb to get it >> working. Just boot from the CentOS cd1 into linux rescue mode, and it >> should autodetect your system and mount it under /mnt/sysimage. >> Once you're in, >> chroot /mnt/sysimage >> /sbin/grub --> you get a prompt grub> >> >> In my case I read in my grub.conf: >> title CentOS (2.6.9-22.0.2.106.unsupportedsmp) >> root (hd0,0) >> >> so at the grub> prompt I would type >> >> grub> root (hd0,0) >> grub> setup (hd0) >> grub> quit >> >> You can then exit, reboot and your system should be up and running. >> >> Hope this helps >> > > Thanks Simone, > It works now. Anyway, can you give me an insight how RAID-5 works in > preventing the loss of data? > > I'm testing it by copying a large file (20MB) into /root, and when I unplugged > a drive, it seems that the data is still Ok. How does RAID-5 do this? > > Thank you, > It uses parity information that it stores across all three drives. In your setup 1/3 of each drive is used for the parity information. Basically any two drives then have enough parity information to recreate the date on the third drive. With raid 5 the usable storage is C * (N -1) where C is the capacity of the drives and N is the number of them. So if you have 3 * 250GB disks the usable storage is 500GB. If two disks die at the same time kiss all your data good bye (although this is a pretty rare scenario)