Mark Knecht wrote: >I need to learn the RAID levels, but what I mean is I think what's >called mirroring. >
Yep, thats RAID1. Forgive me, I've been married to my laptop for too long, and I forget that 'normal' computers can have multiple 1394/USB controllers! In that configuration, yes, you should be able to get some decent bandwidth. If/when you do try this, please report the results. I am using USB2.0 disks for my backups right now, but my bandwidth is limited to 20MB/sec total. Since one of the disks I backup is also a USB2.0 disk, my effective bandwidth is about 10MB/sec for much of my backup (transfer from USB2.0 disk to memory, memory to other USB disk). I also have a 1394 port that I am not using for anything right now, and I know that if I moved one or the other to that bus, I could get some more speed. But I am not sure which one to move, because I don't know whether it is faster or slower than the 20MB/sec maximum that I get now. >Two or more drives with identical data for >redundancy. In my case I have three 1394 controllers in the same >machine. I was considering putting identical drives on each cable in >parallel so the 1394 bandwidth is essentically trippled and the same >data is written and read to all drives. Seems to me the only overhead >is then 3x disk bandwidth across the PCI bus as well as the >verification that all 3 drives return the same data. > > I am pretty sure that when reading data, the kernel's software RAID treats the the array the same as RAID0..that is it would read all 3 disks simultaneously, but different blocks from each, to maximize throughput. If the array is 'clean', and all 3 disks contain the same data, there is no point in reading the same data from all 3 drives. Write performance suffers slightly with RAID1, because you basically have to wait for the slowest disk. Even if they are all the same speed, there is always one that lags a few ms because the platters are not synchronized. For the filesystem, I say choose your favorite. Just remember that 3 copies of the same mistake doesn't help you much...you still need backups! -Richard -- gentoo-user@gentoo.org mailing list
