Re: Raid 0+1 is using a lot of CPU?

> I just found out some info... in Ahmed Alomari Book on page 105 he
> says that "the performace loss caused by mirroring is approximately 15
> percent".

> >My sysadmin tells me that my 0+1 implementation will use up to 1/3 of
> >machine's CPU resources.. is this true?

First, the 15% performance loss is specifically I/O performance loss, and only during writes! There is actually a performance gain when reading from mirrored or mirrored/striped volumes. For a 8 disk 0+1 system, you can expect about 15% write performance loss and about a 6 or 7 times read performance gain.

Software-based RAID (from Volume Manager or DiskSuite) are not CPU intensive. Even RAID-5 is easy on the CPU. The only CPU overhead there is for RAID 0+1, is that your system issues two writes instead of one. With RAID-5, the processor also has to calculate parity for each write. In one second on a 333Mhz UltraSparcII processor, well over 400 million XORs can be calculated. In a given second, even the busiest of system won't ever have to calculate parity more than a few hundred times.

Anytime you have the disks, use 0+1. There is no reason not to.

Regards,

Andrew Garman
Goliath Networks, inc. Received on Wed Sep 01 1999 - 11:56:18 CDT