[CentOS] Re: RAID, LVM, extra disks...

Thu Nov 29 18:39:16 UTC 2007
Ugo Bellavance <ugob at lubik.ca>

Ross S. W. Walker wrote:
> Ugo Bellavance wrote:
>> Ross S. W. Walker wrote:
>>> What are you trying to accomplish storage wise?
>>> Is this for commerical or personal use?
>> Commercial, but non-critical use.
>>> If for personal use, then it isn't as critical how it is 
>> setup, but if 
>>> this is for commercial use then you need to target your storage to 
>>> your application.
>> Nothing really very IO demanding.  Running an OpenVZ server 
>> with many Virtual machines on it, but load is very low.
>>> If you want this to be reconfigured on the fly without ever 
>> rebooting 
>>> then you may find your options limited on which RAID levels you can 
>>> choose.
>>> Typically I keep the system disks in a RAID1 and the data disks on 
>>> separate RAID arrays setup depending on the application.
>>> Scratch or temp files -> RAID0
>>> File serving -> RAID5 or RAID6 (depending on disk size # of disks) 
>>> Databases, large email, many VMS -> RAID10
>>> Let us know what you want the storage for and we can suggest a 
>>> configuration.
>>> Top of my head though, I would use the 18GB for the OS and 
>> keep the 4 
>>> 36GB for application data either as a RAID10 or RAID5.
>> That would make sense.  Use RAID1 18GB for /, /boot and /var and use a
>> RAID4 with 4 36GB HDD for /vz (OpenVZ's virtual machines are 
>> located there).
>> Makes sense?
> Makes sense to me, I have found in my environment that VMs generate a
> lot of random io, so a RAID10 may be better suited, though it means
> 72GB of useable space instead of 108GB.

I understand, but my IO is not very significant...  I think I'll use the 
RAID5 for /vz/

> Also by using growing or sparse files for the vz images, a volume can get
> fragmented pretty quickly. To minimzie that from happening, think about
> creating LVs with separate small file systems to hold each vz image. If
> the LVs start running out of space, you can grow them and the file
> system as needed which will reduce the fragmentation tremendously.
> You will still end up with LV extents fragmented, but since they are
> larger it isn't as serious a performance issue.

OpenVZ doesn't work with vz image.  It works as a regular filesystem.

Thanks a lot for your advice.