RAID 0

Would raid zero be the best choice for my home filesharing server?? I heard somewhere that if you have a 5gig 5400 rpm on the same line as a 40 gig 7200 rpm the fastest speed would be 5400rpm and 10 gig... would this be true? can someone explain some of this stuff to me? thanks

Interested in that mirror setup if you dont mind explaining.

A RAID array is a means of combining several physical disks and having them function as one, while giving up the capacity of one or more physical disks to store redundancy info. The redundancy info helps save your data if one drive in the array fails.

There are a couple of ways data can be arranged in a RAID array. One is mirroring, where multiple drives all have the same contents. Another is striping, where one disk holds a block of disk data, the next disk holds the next block, and so on, starting the next stripe after storing data on the last drive.

RAID0 is technically not really RAID; it doesn't store any redundancy info, it just stripes your data across multiple drives. This gives you fast access for large blocks of data, since small parts of the data can be gathered from multiple drives at the same time, instead of having to read everything from one drive. RAID0 is the fastest RAID type in existence; the problem with RAID0 is that if one drive fails, all your data is trashed--and the chances of one out of <i>five</i> drives failing is 5x the chances of one out of <i>one</i> drive failing.

RAID1 uses mirroring to maintain redundancy. It's typically done with two drives. Reading is often faster for large blocks, but writing is slightly slower.

RAID2 is an old and not-often-used RAID type; it uses a Hamming ECC code to store redundancy, which requires (log[base2] <i>x</i> ) drives for redundancy, where x is the number of drives <i>not</i> used for redundancy. (if the log bit is confusing, think of it as <i>x</i> redundancy drives for (2 to the power of <i>x</i> ) data drives.) I don't remember how exactly Hamming ECC is done, except that it's a major pain to implement. RAID2 is generally slower and less space-efficient than other RAID types; most new RAID controllers don't support it at all.

RAID3 uses striping with a block size equal to 1 bit. One drive in the array is used to store <i>parity</i> for the drives. Parity defines whether an even or odd number of bits in a set are currently 1; if one drive in a RAID3 fails, the data can be rebuilt using parity calculations. Maintaining and checking this parity information takes a good deal of CPU power, though, and results in one drive in the array getting hammered all the time. You'll spend a lot of time waiting on that one drive that stores the parity info, making RAID3 generally slower than RAID1 or RAID0. It's also the kind of RAID array you really should get a dedicated hardware RAID controller for (i.e. a Promise or 3ware card). The advantage this has over RAID1 is that it stores redundancy info in a more space efficient manner. Getting an 180GB RAID1 requires 360GB space total, with half given over to redundancy, no matter what each drive's capacity is. Getting a 180GB RAID3 made out of 18GB drives merely requires 198GB space total (10 18GB drives, plus one for redundancy).

RAID4 supersedes RAID3 by allowing stripe sizes greater than one bit. It still has the problem of one drive getting pegged all the time though.

(/me stops to draw breath. Deep breath...ahhhhh.)

RAID5 is basically the same as RAID4, except that it alleviates the problem of one drive getting pegged all the time by "rotating" the parity drive. For the first stripe, drive 1 might be the parity drive; for the second stripe, drive 2 would be the parity drive; for the third stripe, drive 3....and so on. Since RAID5 supersedes both RAID3 and RAID4, most RAID controllers don't support RAID3 and RAID4 anymore.

There's also RAID10 (0+1) and RAID50 (0+5). RAID10 is basically a set of RAID1 arrays striped together into a RAID0, or a pair of RAID0 arrays mirrored as a RAID1. RAID50 is basically the same concept; one RAID arrangement on top of another.

(At some point, I remember reading that either ANSI or the T13 committee was designing RAID6 and RAID7. Haven't heard of anything on those new RAID types in years. Anybody hear about that?)

One problem with combining several drives in a single RAID array is that the size of the smallest drive is treated as the maximum usable capacity of any drive--i.e. if you put a 3GB and a 10GB in a RAID array, only 3GB of the 10GB drive will be used. The other 7GB will go to waste. Speed is limited in the same manner as well; you're just as well off RAIDing two 5400RPM drives as RAIDing a 5400RPM and a 7200RPM--except you probably spent a bit more on the 7200RPM drive .

Kelledin

"/join #hackerz. See the Web. DoS interesting people."

ja...I didn't actually notice how long it was getting...till I went to post it. Then I had to go back and edit about five or six things =/

Kelledin

"/join #hackerz. See the Web. DoS interesting people."

What are other options for large data storage?

could somone list multiple methods? thanks

becase basicly all i need is like an array for 4+ harddrives... I'm just looking for a format to set them up.. since a regular IDE system isnt going to cut it.

Well, it doesnt matter for the speed.. i just want to store ALOT of stuff and pick what i want to see over my LAN

Western Digital has 80gb 7200rpm drives for around $185. You can't beat that for mass storage! Technically you could run 7 of those plus a CD-Rom on a motherboard like the KT7A-Raid.

-- Ah sh*t! sys64738 --

You can have both IDE and SCSI drives in the system. Being able to boot one or the other depends on a couple of things:

1) To boot off a drive connected to a SCSI controller, the SCSI controller needs to have an onboard BIOS chip. If the
controller doesn't have an onboard BIOS, you can still use SCSI drives on it, you just can't boot from them.
2) There's normally a section in the BIOS where you can set the boot device order; it's usually set to "A:, C:, CDROM" or "A:, C:, SCSI".

Kelledin

"/join #hackerz. See the Web. DoS interesting people."