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)
