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3 Hard Drives?

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jcw122

Member
Joined
Jun 25, 2004
I'm new to the physical make up of computers. My question is: What is the point of having 3 different hard drives? And what does this do to ur comp compared to having 1 or 2? Sry if this is a noob question, im just trying to understand what im dealing with so i can eventally build/mod my first comp.
 

stui_nz

Member
Joined
Feb 8, 2003
Location
New Zealand
The things you need to know about hard drives are:
They have limited storage space.
They have a limited speed. ~50Mb/s
And they are prone to failure once in a while.

People with multiple hard drives are typically looking to address these issues - ie. more storage space, data backup and improved performance/security through a raid configuration.
 

JigPu

Inactive Pokémon Moderator
Joined
Jun 20, 2001
Location
Vancouver, WA
Not a stupid question if you haven't been following the storage crowd :) RAID stands for "Redundant Array of Independant Disks" and is a way of having multiple drives act as one as far as the computer is concerened. Through RAID, you can increase reliability (RAID level 1 increases reliability by having one drive mirror another), capacity (All RAIDs but level 1 have more capacity than any single drive in the array), or speed (RAID 0 takes two drives and splits data evenly between the two for theoretically 2x the data rate) by basically squishing multiple drives into one.

JigPu
 

Tatuya

Member
Joined
Mar 4, 2004
Location
Crunching [email protected]
Don't forget to point out that in RAID 0 if one drive of the RAID set fails you lose ALL data and have no chance of recoverey, hence many people using backup drives which I have yet to purchase.
 

Drec

Member
Joined
May 23, 2004
JigPu said:
Not a stupid question if you haven't been following the storage crowd :) RAID stands for "Redundant Array of Independant Disks" and is a way of having multiple drives act as one as far as the computer is concerened. Through RAID, you can increase reliability (RAID level 1 increases reliability by having one drive mirror another), capacity (All RAIDs but level 1 have more capacity than any single drive in the array), or speed (RAID 0 takes two drives and splits data evenly between the two for theoretically 2x the data rate) by basically squishing multiple drives into one.

JigPu

well said...example..if in a RAID 0 your saving a large file thats lets say 1GB..instead of saving it all to one drive which may take 5 seconds it splits it into 2 500MB portions and saves each on a diffrent drive simotaniusly(sp)..which effectivly cutts the time it takes to read / write data..

and a RAID 1 is effective for backiing up drives..2 drives that are exactly the same w/ same info on them so if one crashes your safe because you still have another with all the same stuff as the one that crashed. :D
 

JTanczos

Member
Joined
May 7, 2004
Location
Eastern Pennsylvania
Raid 3, 4, 5 and 6 are good mix of space vs fault tolerance(1 drive crashes you dont loose info). Raid 3 and 4 write data to all but one of the drives in pieces. Meaning placing segments or blocks to different drives in order similar to raid 0. 64 bits or 1 block to drive A, 64 bits of 1 block to Drive B and so on until it gets back to drive A.

Now on the last drive of the array(Name for all drives when they are actually connected through raid) holds info called "parity bit"(Its a calculation of the drives to get a final number). Example Drive A writes a 1 and drive B writes a 0. 1+0=1 so the parity bit =1 and that is written to the 3rd drive. So if drive A or B should happen to fail the raid array can be rebuilt using the information from the remaining drive along with the Parity bit by using subtraction. Problem with those is the Parity drive can eventually be slow as molasses in January when writing to the other drives because all the calculations have to be written on the one drive which is written at its normal slow speed while the others are working at "twice" the speed.

Raid 5 takes care of this by splitting up the parity bits into groups among the different drives. Instead of 1 drive being dedicated to the parity bits they are spread through out the drives. Faster speed.

Any of the above can be expensive to implement and you need at least 3 drives for these to work. Also you will always loose one drive to the parity bit on 3,4,5. (D*S)-S=TS where d= number of drives, S=Drive space and TS = Total space. 3 drives of 120 megs would be (120*3)-120=240. Total space would be 240 but your data would be allot safer than raid 0 which has NO fault tolerance.

Raid 6 has better fault tolerance by having 2 parity bits. Unfortunately you loose 2 drives. (D*S)-2S=TS. 4 120 gig drives (4*120)-2*120=240. With this one you can loose 2 drives and still be able to repair your information. Raid 6 is also expensive as it takes a strong raid processor to work.

*chuckles* Now that I confused the hell out of you, you can learn more here http://www.bytepile.com/raid_class.php They have pictures also.

JT
 
Last edited:

Sjaak

Member
Joined
Apr 26, 2004
Location
The Netherlands
Good explanation, still.

I'm going to build RAID soon, but everytime again i read the story of RAID-0 failing, i get scared again :(
 

ggo

Disabled
Joined
Jun 27, 2004
get a tape drive to backup your data. or better yet, become more apathetic towards your data. its what i do, and i love to charge ahead with no fear.
 

Sjaak

Member
Joined
Apr 26, 2004
Location
The Netherlands
ggo said:
get a tape drive to backup your data. or better yet, become more apathetic towards your data. its what i do, and i love to charge ahead with no fear.

Until one of your raid0 drives crashes :cry:

happened last year, i had 2x40GB seagate in RAID, and one of them started hicking on heavy load. Managed to copy about half the data before it died.
 

kiyoshilionz

Member
Joined
May 20, 2004
Location
Wheaton, IL
I'll give you a more simple answer, only concerning RAID 0 and RAID 1, since they're the most basic and most commonly used by regular people like us.

Let's say you have two 120GB hard drives. If you want more speed, but can risk losing all your data when something goes wrong (unless you have a 3rd backup hard drive) you can go with RAID 0. Like people have said above, it will put part of the file on each hard drive, so when you want to open it, it will open it from both hard drives at once, speeding things up.

If you really can't afford to lose data or you don't need all the space provided by your hard disks, then use RAID 1. It basically writes everything to BOTH hard drives, so it makes copies of every single file. When one disk crashes, just pull it out, put another one in, and it'll still run smoothly. But then your 120GB + 120GB becomes only 120GB since you're storing backups of every single file on your system.
 

Sjaak

Member
Joined
Apr 26, 2004
Location
The Netherlands
I was wondering...could they invent a new RAID mode, based on this:


You have 2 drives, same, X, size. They use striping to improve performance. They are used to read/write the data at any time.

At the same time, you have one drive, size 2X, that contains all data from drive 1 and 2, but unstriped, as a backup. He is only used in idle time to write all data on it, not for reading. In case one of the harddisks crashes, you have a backup. In case of heavy load, he can provide more speed by reading the data as well (kind of a three-drive striping then)

Like 2x 80GB striping thereby 1x160GB for the backup.

This doesnt save more space (overhead is still 100%), but it saves more money and space (the bigger drive is cheaper per Gbyte, and you dont have 4, but 3 drives), and it is faster in reading then RAID0 because of the 3-drive read option.

Theres also no need for parity or XOR or whatsoever chips, cause striping can be done by the most simple RAID adapter. The only thing to be programmed is the 'auto-backup' function on idle times, and the ability to read from 3 drives at a time.
 

Mr.Radar

Member
Sjaak said:
I was wondering...could they invent a new RAID mode, based on this:


You have 2 drives, same, X, size. They use striping to improve performance. They are used to read/write the data at any time.

At the same time, you have one drive, size 2X, that contains all data from drive 1 and 2, but unstriped, as a backup. He is only used in idle time to write all data on it, not for reading. In case one of the harddisks crashes, you have a backup. In case of heavy load, he can provide more speed by reading the data as well (kind of a three-drive striping then)

Like 2x 80GB striping thereby 1x160GB for the backup.

This doesnt save more space (overhead is still 100%), but it saves more money and space (the bigger drive is cheaper per Gbyte, and you dont have 4, but 3 drives), and it is faster in reading then RAID0 because of the 3-drive read option.

Theres also no need for parity or XOR or whatsoever chips, cause striping can be done by the most simple RAID adapter. The only thing to be programmed is the 'auto-backup' function on idle times, and the ability to read from 3 drives at a time.

But the whole point of RAID-0 is to get 2x the theoretical write speed of each individual drive, but since you have a third drive working at 1x the other two drives would have to slow down to 1x. Also, you could just do RAID 0+1 where it creates two striped arrays, one mirroring the other, though this would require 4 drives of the same capacity.
 

Sjaak

Member
Joined
Apr 26, 2004
Location
The Netherlands
In what i said, i meant that the 3rd drive would be only for backup purposes, in idle time. (eg. when the pc is idle, only then the data from the striped array is copied) Whenever lots of speed is needed in reading however, he can jump in and support the striped array by providing a 3rd location where the data is to be found.
 

JCLW

Member
Joined
Apr 1, 2002
jcw122: Welcome to the Forums! :)

I run three drives - one for OS and applications, and another two in a RAID 1 (mirrored) array for data. All the mirroring is handled by the RAID card, so windows just sees two hard drives: C: (OS & apps), and D: (data).
 

Sjaak

Member
Joined
Apr 26, 2004
Location
The Netherlands
JCLW said:
I run three drives - one for OS and applications, and another two in a RAID 1 (mirrored) array for data. All the mirroring is handled by the RAID card, so windows just sees two hard drives: C: (OS & apps), and D: (data).

Why the choise for RAID-1? (just curious)
 

Sjaak

Member
Joined
Apr 26, 2004
Location
The Netherlands
Mr.Radar said:
Because if one drive dies your data doesn't go with it. I'd be running a RAID-1 array if I could afford it.

Yes but you lose half the storage space...And the chance one drive fails is very small, yes, two drives is an increase, but still, very small.

For me RAID1 is a waist of money.