Pages: 1

 

2008-02-24 01:51:45
[TUF]Whiskey_Oktober
mmmm...Toasty!
+91|7000|Oregon
i had 2 80GB harddrives in raid until just a few days ago when one of them decided to die (probably had something to do with my sister kicking my computer in a fit of rage...long story). but anywho, i was skeptical of the whole RAID thing from the start, but i have a few questions now...

whats the benefit of RAID 5 over RAID 1/0?  can you run a RAID 5 array with 3 drives or does it have to be 4? is raid worth it at all, as large capacity hardrives are super cheap these days?

im kinda ignorant when it comes to stuff like this, so hopefully someone can give me some insight.
2008-02-24 02:05:29
Gawwad
My way or Haddaway!
+212|6963|Espoo, Finland
As far as I know, RAID 5 uses two HDD's in RAID 0 and one in RAID 1 for backing up.
Should work with 3 HDD's, though I'm not sure what happens when the RAID 0 exeeds the space of the RAID 1 HDD.
2008-02-24 02:12:14
mikkel
Member
+383|6879
The main benefit of RAID 5 over RAID 0 is that you get the added protection of being able to lose a drive without catastrophic data loss. The benefit over RAID 1 is that you only lose a third of your space, not half of it, while getting just shy the throughput of a RAID 0 array at average loads with typical read/write distribution.

You need at least three disks for a RAID 5 array - three data disks with distributed parity. If you were to do it with two disks, you'd essentially have RAID 1.

RAID is definitely worth it if you have the money. Which level to run depends on your budget and how much you value your data. RAID 0 is asking for trouble, and RAID 1 is useful only if you can't afford more than two disks. Next step up is RAID 5, which is what most people do for home use, as RAID 5 is best on a budget. If you want to go all out and avoid the performance penalties incurred from calculating and writing the block parity in a RAID 5 setup, you'll want to stack a RAID 0 array on top of a RAID 1 array for RAID 01/10/1+0/whatever they choose to call it today. That, however, takes at least 4 disks, and it's not really applicable for your average home setup.

Gawwad wrote:

As far as I know, RAID 5 uses two HDD's in RAID 0 and one in RAID 1 for backing up.
Should work with 3 HDD's, though I'm not sure what happens when the RAID 0 exeeds the space of the RAID 1 HDD.
RAID 5 works with the principle of parity. RAID 5 is block level striping, but it's easier to explain at the bit level, so here goes.

You have 5 disks in a RAID 5 array, A, B, C, D and E. In this example, we're focusing on one bit, parallel across the disks. We're going to go with these values:

Code:

A - 1

B - 0

C - 1

D - 1

E - Parity.
Now, E holds the parity for this particular bit, so we need to calculate the parity based on the values on the remaining disks. This is done with a boolean XOR calculation. The truth table for XOR looks like this:

Code:

A B | Y
0 0 | 0
0 1 | 1
1 0 | 1
1 1 | 0
The calculation we're performing on these is (((A XOR B) XOR C) XOR D) = E, or, with our values applied, (((1 XOR 0) XOR 1) XOR 1) = E.

(((1 XOR 0 =) 1 XOR 1 =) 0 XOR 1) = 1. That means that E, our parity, is 1.

Our values are now:

Code:

A - 1

B - 0

C - 1

D - 1

E - 1
Now, suppose we lose disk C. Oh noes. What do we do? Well, having these values

Code:

A - 1

B - 0

C - ?

D - 1

E - 1
, we simply omit drive C from the calculation, and append an XOR of the parity at the end. That is, (((A XOR B) XOR D) XOR E) = C. Performing the calculation, we get (((1 XOR 0 =) 1 XOR 1 =) 0 XOR 1) = 1! Tadaa! We've gotten the value of C, thanks to the magic of the XOR gate. That's how parity works in RAID arrays.

Last edited by mikkel (2008-02-24 02:25:49)

2008-02-24 02:23:16
kylef
Gone
+1,352|6771|N. Ireland
RAID5 - 3 Drives. One drive of size 2/3s all hard drive space in RAID array shows in Windows. Offers speed and protection - RAID0+1 almost.
2008-02-24 04:39:22
Bertster7
Confused Pothead
+1,101|6860|SE London

mikkel wrote:

Next step up is RAID 5, which is what most people do for home use, as RAID 5 is best on a budget. If you want to go all out and avoid the performance penalties incurred from calculating and writing the block parity in a RAID 5 setup, you'll want to stack a RAID 0 array on top of a RAID 1 array for RAID 01/10/1+0/whatever they choose to call it today.
Nice post, in general. But I disagree with this bit.

RAID5 is not used commonly by home users as it is the most expensive to implement on a small scale. RAID0, RAID1 and sometimes combinations of them such as RAID 0+1 and 1+0, which are not quite the same thing, can be implemented through software RAID, which is what home users tend to have (onboard Mobo RAID). RAID5 cannot, as far as I know, be implemented through software RAID and requires additional hardware (a proper RAID card) which will be substantially less cost effective for virtually all home usage scenarios.
2008-02-24 05:01:23
mikkel
Member
+383|6879

Bertster7 wrote:

mikkel wrote:

Next step up is RAID 5, which is what most people do for home use, as RAID 5 is best on a budget. If you want to go all out and avoid the performance penalties incurred from calculating and writing the block parity in a RAID 5 setup, you'll want to stack a RAID 0 array on top of a RAID 1 array for RAID 01/10/1+0/whatever they choose to call it today.
Nice post, in general. But I disagree with this bit.

RAID5 is not used commonly by home users as it is the most expensive to implement on a small scale. RAID0, RAID1 and sometimes combinations of them such as RAID 0+1 and 1+0, which are not quite the same thing, can be implemented through software RAID, which is what home users tend to have (onboard Mobo RAID). RAID5 cannot, as far as I know, be implemented through software RAID and requires additional hardware (a proper RAID card) which will be substantially less cost effective for virtually all home usage scenarios.
Ah, I wasn't being clear. What I meant was that RAID 5 is used much more frequently than other RAID levels when going beyond simple 0/1. RAID with parity in general isn't good to implement in software, as it'll hog CPU on every write. You really need dedicated processors to offload most high-intensity I/O related operations like checksum and parity calculations and line encoding.
2008-02-24 05:11:37
Bertster7
Confused Pothead
+1,101|6860|SE London

mikkel wrote:

Bertster7 wrote:

mikkel wrote:

Next step up is RAID 5, which is what most people do for home use, as RAID 5 is best on a budget. If you want to go all out and avoid the performance penalties incurred from calculating and writing the block parity in a RAID 5 setup, you'll want to stack a RAID 0 array on top of a RAID 1 array for RAID 01/10/1+0/whatever they choose to call it today.
Nice post, in general. But I disagree with this bit.

RAID5 is not used commonly by home users as it is the most expensive to implement on a small scale. RAID0, RAID1 and sometimes combinations of them such as RAID 0+1 and 1+0, which are not quite the same thing, can be implemented through software RAID, which is what home users tend to have (onboard Mobo RAID). RAID5 cannot, as far as I know, be implemented through software RAID and requires additional hardware (a proper RAID card) which will be substantially less cost effective for virtually all home usage scenarios.
Ah, I wasn't being clear. What I meant was that RAID 5 is used much more frequently than other RAID levels when going beyond simple 0/1. RAID with parity in general isn't good to implement in software, as it'll hog CPU on every write. You really need dedicated processors to offload most high-intensity I/O related operations like checksum and parity calculations and line encoding.
Glad we cleared that up.

But then how many home users are going to be spending £200+ on a 4 port SATA RAID card?

Software RAID is still beneficial. Just not so much. Although good hard drive management, with good partial stroking practices and big drives, is the best way to get decent performance for home users.

I do a lot of messing about with HD movie files. I do all of that on a big software RAID0 setup, because of the good block transfer rates and the benefits far outweigh the CPU time wasted (especially with CPUs with either 4 or 8 cores (I use a lot of 8x Mac Pros - even if they do perform abysmally for the price, you'd think with 2 Woodcrests running together they'd go fast, but no)).
2008-02-24 05:25:55
=Karma-Kills=
"Don't post while intoxicated."
+356|6862|England

Gawwad wrote:

As far as I know, RAID 5 uses two HDD's in RAID 0 and one in RAID 1 for backing up.
Should work with 3 HDD's, though I'm not sure what happens when the RAID 0 exeeds the space of the RAID 1 HDD.
No. Just... no.

[TUF]Whiskey_Oktober wrote:

whats the benefit of RAID 5 over RAID 1/0?  can you run a RAID 5 array with 3 drives or does it have to be 4? is raid worth it at all, as large capacity hardrives are super cheap these days?
RAID1 offers redundancy, at the cost of loosing half your HDD's. (Min 2 Drives)
RAID0 offers speed, but is techinically NOT a form of RAID (more AID!) as it offers no redundancy. (Min 2 Drives)
RAID5 offers a comprimise between both, and is used quite widely in database servers. Speed and redundancy. However, RAID5 isnt normally seen in home setups as for the best results you need a decent (£200+) RAID controller card, and ideally SAS drives. (Min 3 drives).

(Theres a load more levels, as well as nested levels - 0+1 and 1+0, but you wont need to worry about these unless youve got a ton of cash to build a mission ciritcal server).
2008-02-24 17:34:47
jaymz9350
Member
+54|6855

Bertster7 wrote:

mikkel wrote:

Next step up is RAID 5, which is what most people do for home use, as RAID 5 is best on a budget. If you want to go all out and avoid the performance penalties incurred from calculating and writing the block parity in a RAID 5 setup, you'll want to stack a RAID 0 array on top of a RAID 1 array for RAID 01/10/1+0/whatever they choose to call it today.
Nice post, in general. But I disagree with this bit.

RAID5 is not used commonly by home users as it is the most expensive to implement on a small scale. RAID0, RAID1 and sometimes combinations of them such as RAID 0+1 and 1+0, which are not quite the same thing, can be implemented through software RAID, which is what home users tend to have (onboard Mobo RAID). RAID5 cannot, as far as I know, be implemented through software RAID and requires additional hardware (a proper RAID card) which will be substantially less cost effective for virtually all home usage scenarios.
just so you know raid 5 can be done with motherboard sata ports, my board will do it and i've seen others. what limist most motherboards is having enough ports on one controller to do raid 5.  my last board had 4 sata ports but on 2 ontrollers. my new board has 6 sata ports, 4 on one controller and 2 on another and is raid 5 capable.
2008-02-24 17:37:12
Mutantbear
Semi Constructive Criticism
+1,431|6243|London, England

Haffeysucks' hard drive just failed and now he has been waiting for a new one for at least 2 weeks. I dont think he was using a raid though. I never thought the idea of a RAID was very appealing to me
_______________________________________________________________________________________________ https://i.imgur.com/Xj4f2.png
2008-02-25 10:51:11
Bertster7
Confused Pothead
+1,101|6860|SE London

jaymz9350 wrote:

Bertster7 wrote:

mikkel wrote:

Next step up is RAID 5, which is what most people do for home use, as RAID 5 is best on a budget. If you want to go all out and avoid the performance penalties incurred from calculating and writing the block parity in a RAID 5 setup, you'll want to stack a RAID 0 array on top of a RAID 1 array for RAID 01/10/1+0/whatever they choose to call it today.
Nice post, in general. But I disagree with this bit.

RAID5 is not used commonly by home users as it is the most expensive to implement on a small scale. RAID0, RAID1 and sometimes combinations of them such as RAID 0+1 and 1+0, which are not quite the same thing, can be implemented through software RAID, which is what home users tend to have (onboard Mobo RAID). RAID5 cannot, as far as I know, be implemented through software RAID and requires additional hardware (a proper RAID card) which will be substantially less cost effective for virtually all home usage scenarios.
just so you know raid 5 can be done with motherboard sata ports, my board will do it and i've seen others. what limist most motherboards is having enough ports on one controller to do raid 5.  my last board had 4 sata ports but on 2 ontrollers. my new board has 6 sata ports, 4 on one controller and 2 on another and is raid 5 capable.
Which board? That is extremely unusual.

It has nothing to do with how many SATA ports are on each controller. Most top end boards have 4 per controller.
2008-02-25 10:55:34
Catbox
forgiveness
+505|6994
me...1 drive... no probs...  whiskey noob... 2 drives... problem... lol
Love is the answer
2008-02-25 11:08:58
max
Vela Incident
+1,652|6846|NYC / Hamburg

[TUF]Catbox wrote:

me...1 drive... no probs...  whiskey noob... 2 drives... problem... lol
me 6 drives, soon 8, no probs ...
once upon a midnight dreary, while i pron surfed, weak and weary, over many a strange and spurious site of ' hot  xxx galore'. While i clicked my fav'rite bookmark, suddenly there came a warning, and my heart was filled with mourning, mourning for my dear amour, " 'Tis not possible!", i muttered, " give me back my free hardcore!"..... quoth the server, 404.
2008-02-25 11:56:01
aimless
Member
+166|6403|Texas
How is RAID 0 faster? Is it because both disks are working to pull up a piece of information?

Also, I have two 160GB drives, one SATA, one PATA, I'm guessing I won't be able to set these in RAID?
2008-02-25 12:08:00
steelie34
pub hero!
+603|6659|the land of bourbon

aimless wrote:

How is RAID 0 faster? Is it because both disks are working to pull up a piece of information?

Also, I have two 160GB drives, one SATA, one PATA, I'm guessing I won't be able to set these in RAID?
easiest way to think of raid 0 is that files are broken down into 2 parts and both parts are written to the disks simultaneously (or three or more depending on how many disks are in the set.)  it is much faster than writing one file to one disk. 

as for your 2nd question, i don't think u can do that with a hardware solution, i think the controllers have to be the same.  software might be able to do it, but i wouldn't recommend as it is very resource intensive.

and to everyone else, RAID 5 isnt any more of less expensive to implement.  it's more cost effective, because you don't lose as much space as you would by mirroring.  if your mobo has a built-in raid controller, and you have more than two disks, i would definitely use a raid 5 volume.

Last edited by steelie34 (2008-02-25 12:09:31)

https://bf3s.com/sigs/36e1d9e36ae924048a933db90fb05bb247fe315e.png
2008-02-25 19:20:26
jaymz9350
Member
+54|6855

Bertster7 wrote:

jaymz9350 wrote:

Bertster7 wrote:


Nice post, in general. But I disagree with this bit.

RAID5 is not used commonly by home users as it is the most expensive to implement on a small scale. RAID0, RAID1 and sometimes combinations of them such as RAID 0+1 and 1+0, which are not quite the same thing, can be implemented through software RAID, which is what home users tend to have (onboard Mobo RAID). RAID5 cannot, as far as I know, be implemented through software RAID and requires additional hardware (a proper RAID card) which will be substantially less cost effective for virtually all home usage scenarios.
just so you know raid 5 can be done with motherboard sata ports, my board will do it and i've seen others. what limist most motherboards is having enough ports on one controller to do raid 5.  my last board had 4 sata ports but on 2 ontrollers. my new board has 6 sata ports, 4 on one controller and 2 on another and is raid 5 capable.
Which board? That is extremely unusual.

It has nothing to do with how many SATA ports are on each controller. Most top end boards have 4 per controller.
I have an ABIT IP35-PRO. But I also know the DFI SLI-DR also supports it. I know I have seen others also just don't remember the model.

 

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