4 hdds in parallel
 

hey, is it possible to use 4 different harddisk drives parallel with the size of the smallest? like mirroing the first 120gb over the three devices and using the rest of each drive as different, single partitions? and if it is, does the data read-speed increase about 4times compared to one single drive?

everything in software? lvm or so?

What you're talking about is striping and there is no mirroring involved, if you're looking for data redundancy with a performance increase you need to look at mirroring and striping (RAID 1/0). You could also do RAID5 or RAID50 depending on the IO operations profile you need. You can do that in software although you will probably want to exclude your boot partition from being part of the array. I generally suggest hardware raid over software, but it is possible to do it in software.

Just curious: Do you need identical hdd devices for hw raid?

I recommend software RAID over hardware RAID, and no RAID at all over the former two.

Anyway, check the wiki for the various types of RAID and the costs and benefits and other stuff:
http://en.wikipedia.org/wiki/RAID

No, you will not get linear scalability with RAID. You will not get 4 times the speed, not even close, for various reasons.

The purpose of RAID is NOT speed but redundancy and theoretically reliability (practically not really).

AID0 is the only one to be recommended for somewhat significant performance gain, but the loss of reliability is usually not worth it, unless you design it as such. Put volatile data on the AID0 and keep a separate HDD for important data.

Yes on all of the raid controlers I regularly deal with.

I universally disagree with this post in its entirety due to misinformation.

There is no problem with TRUE hardware raid (no driver required). The problem is that virtually all the motherboard raid and most sub $300(?) raid cards are fake raid(just google it). In the long run you are usually better off using soft raid rather than fake raid.

Raid0 does give you a significant speed increase (well below 2X) but when it does fail(not if) there is no redundancy. As long as you understand this and back up anything that is critical, raid0 is fine. The other raid solutions do give you redundancy and CAN give you limited speed increases. However, if you are trying this with old drives it is usually more cost effective to just buy the newer, faster, larger drives to start with.

ok, good ... care to rectify it, or just leave it at that ?

I would also recommend software raid over hardware raid as well but purely based on the costs of true raid only. In reality hardware is always going to be a bit faster (sometimes) read HERE for some benchmarks for Linux software vs hardware raids. There are times when software is faster. Using no raid is the simplest form and is normally the best option for normal users not looking for performance increases.