[CentOS] RAID 5 setup?

Benjamin Franz jfranz at freerun.com
Fri Mar 26 18:14:18 UTC 2010

Robert Heller wrote:
> I suspect that this is a simular case to what I did: I have a server
> with 4 drives.  I have several (small) RAID1 partitions (/boot, /,
> /usr, /var, etc.) with 4 mirrors and one large RAID5 with three
> partitions and a hot spare (a LVM volumn group, containing /home and
> some other partitions). I would guess that the admin with the "8-way
> RAID1 for the OS" probably also has a 6 or 8 disk RAID5 or RAID6 for
> the bulk of the disks
Yup. 8 way RAID1 for the OS, 8 way RAID6 for the data. I was hoping when 
I setup the 8-way RAID1 for the OS that I would get really good read 
speeds since md is supposed to stripe reads from RAID1, but in practice 
the RAID6 completely kills it for read performance (~61 MB/sec from the 
RAID1 partition vs ~200 MB/sec from the RAID6 partition).

In a deeply ironic turn of events, one of the hard drives in that 
machine died in a way that freaked the hardware controller driver out 
and caused a kernel panic last week. The machine wouldn't finishing 
booting until I physically removed the bad drive. The RAID1 was fine 
afterwards, but the RAID6 had to be manually re-assembled (no 
corruption, it just wouldn't automatically start until I intervened).

Benjamin Franz

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