striping and raid

striping and raid

Post by s.. » Sat, 22 May 1999 04:00:00



I am running 4.3.2 and currently have a filesystem striped across the
center tracks of 4 4.5g SSA drives. I have learned that if a disk is
going bad in this config, I cannot migrate the data to another disk.
What type of config is recommended. The reason for me to use striping
is the obvious one, performance. I would like to maintain the same
performance level if possible. I am using a RAID SSA Adapter, but I
have other SSA disks on the same adapter, but I do not want to disturb
their current config.

Any suggestions?

Thanks in advance

George E Hagopian
Systems Adminstrator
Mediastream, Inc


 
 
 

striping and raid

Post by Phil Langerhol » Sat, 22 May 1999 04:00:00


If you use RAID-5 you will see a drop in your write performance.  RAID-5
uses parity to reconstruct the the data in the event you lose the
drive.  Every time you write to a file on a drive that is configured for
RAID-5, the parity bit will also be updated (if you have the jfslog on
this drive too, then you must update the jfslog and the parity bit for
the jfslog, you would be better off putting the jfslog on a non-RAID-5
drive).  Also, with RAID 5, you will lose 20% of your total disk space
(20% of each disk is allocated for parity).
   You will not disturb the configuration of the other disks if you go
with RAID-5.  You will just need to change the disks you are giong to
use for the RAID from AIX System Disks to Array Candidate Disks and then
create your RAID from there.  If I remember correctly, you need at least
4 disks for the RAID array and, if you are using the enhanced RAID
adapter and you plan on using a hot spare, you must have the hot spare
in the same loop as the drives you have in the RAID configuration.


> I am running 4.3.2 and currently have a filesystem striped across the
> center tracks of 4 4.5g SSA drives. I have learned that if a disk is
> going bad in this config, I cannot migrate the data to another disk.
> What type of config is recommended. The reason for me to use striping
> is the obvious one, performance. I would like to maintain the same
> performance level if possible. I am using a RAID SSA Adapter, but I
> have other SSA disks on the same adapter, but I do not want to disturb
> their current config.

> Any suggestions?

> Thanks in advance

> George E Hagopian
> Systems Adminstrator
> Mediastream, Inc



--
Phil Langerholc - DCS UNIX Systems Support
IBM Global Services - Integrated Supply Chain, Poughkeepsie, NY

The opinions expressed are my own and do not reflect those of IBM

 
 
 

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