RAID?

[061070]

Anyone explain RAD (stripping) and RAID (Mirror).

Not 100% sure exactly what they do.

[NooNoo]

Scuba has written a basic tutorial here that should get you started. From there you can get a basic understanding and be able to research what raid type is right for you

[confus-ed]

Raid Advisory Board: Provides a more 'wordy' version....

Briefly mirroring is creating a duplicate copy of the original data for integrity purposes, striping is 'spreading' data across a number of disks to improve performance, all RAID numbers 0,1..5 & 6??? are a combination of the two techniques.

[Matridom]

[quote]Originally posted by confus-ed:
Raid Advisory Board: Provides a more 'wordy' version....

Briefly mirroring is creating a duplicate copy of the original data for integrity purposes, striping is 'spreading' data across a number of disks to improve performance, all RAID numbers 0,1..5 & 6??? are a combination of the two techniques.

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Not quite.. RAID0 is stripping, spreading across 2 or more dirves WITHOUT parity. You loose a drive, you loose your data...(Total Hard drive space = usable Hard drive space)

RAID1 is mirroring, I.E. Copies the same data to 2 drivers.(Total usable hard disk = 1/2 physical hard drive space)

RAID 3 uses a parity bit on a third hard disk, so you can loose a drive without losing data.(uses logic XOR)(Total usable hard disk = 2/3 physical hard drive space)

RAID5 uses a higher level of parity where the parity bit is spread across the drives(more than 3 drives are used). Again, any drive can die and it can be rebuilt.(Total usable hard disk = 4/5 physical hard drive space if 5 drives are used)

The main advantage to RAID (Redundant Array of Independant Disks) other than data security is the insane read and/or write speeds.

I have a pair of 20 gigs on raid0 and my Write speed is double of a single drive.. Mirroring give you double the read speed, raid 3 and up gives you better on both. A SCSI raid 5 aray has mind boggling bandwith (200 megs/sec ACTUAL througput is not out of the question)

[Gameguru]

[quote]Originally posted by Matridom:
A SCSI raid 5 aray has mind boggling bandwith (200 megs/sec ACTUAL througput is not out of the question)

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We use a 5x9GB ultra wide scsi (160MBps)raid 5 on a Dell power-edge 6500. It has 4 PIII xeon 550s and 2 gigs of ram. The throughput on that machine is undescribable! If I could get 1/4 of that speed off my KG-7, I would be happy!

[confus-ed]

What do you mean not quite , bloody cheeky!! Just a few words then if we are gonna be like that!! I did say briefly....

Raid comes in two varieties software and hardware. You can implement it in your o/s (software) or with a physical thing (hardware)

[quote]Originally posted by Matridom:
The main advantage to RAID (Redundant Array of Independant Disks) other than data security is the insane read and/or write speeds.

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Mmm I'd suggest that this 'apparent' increase has more to do with Your SCSI card & disks and the improved performance of your raid controller over any standard IDE device controller, and at a flying guess the fact you are using a 64 bit PCI bus (In your server?) rather than 32 like the rest of us mortals. You can't get that fast on a normal pc, you just can't move that much data that fast in a 32 bit bus......

Oh - re "I have a pair of 20 gigs on raid0 and my Write speed is double of a single drive.. Mirroring give you double the read speed, raid 3 and up gives you better on both. " - In theory yes, but in practice nothing like (see also later), you are incurring 'extra' overhead by changing the read./write source all the time, so it depends on your disks & controller and I guess O/S as well. Depends what you are 'measuring' too, big fat single file transfers or a billion little ones (like windows!).

So yes multiple disks are preferable to read & write to/from, but that's more to do with the restrictions imposed by a Von Neu-whats-is-face(single control point computers like PCs).

Outside windows world, software raid is used natively in a number of o/s, you do get tremendous improvement but more with more cpu's, you need more processes to take advantage.

You need the right o/s, file system and equipment to realise all the gains. The average gain on a PC just doen't warrant the cost.

For my own PC, personally I'm still a fan of FAT, I've no SCSI cards or disks in sight , no raid either, mind you the biggest I need a partion to be is 1.5 gig, now if I wanted to get data out of a 6 terabyte database I'd have to start thinking differently....

& lastly (hurahh!!) we all forgot to say that RAID might actually make things go slower.....
When you speed your writing you slow your reading & vice versa, I'm off to read my own link now, there's more to this than meets the eye......

[Matridom]

I guess i need to go into a little more detail.

I'm using raid0 in my desktop. I'm using a promise ultra 66 controller that i "Modified" into a fastrack 66 IDE raid controller(total cost, $40 can), you can take a look at the conversion and resulting benchmarks here. I'm using 2 20 gig 5400 rpm drives(one maxtor, one WD) my write on a single 5400 rpm drive on the same controler is at 18-19 meg/sec (NTFS file system, win2k) When the two are raided, i get 36 megs/sec, this is an average througput of both large and small files.

The increase in speed is much greater when you use hardware based raid controllers. Software base raid has a major restrictions, RAID0 cannot be used on the boot partition. you can read an artical, RAID Without Additional Hardware

[confus-ed]

Err I get about 25 with a single 7200, ata 66 disk, what I meant was that I wasn't gonna get 50 (PCI bus).

Obviously shows what chipsets, memory, blah blah can make to any system.

[quote] The increase in speed is much greater when you use hardware based raid controllers. Software base raid has a major restrictions, RAID0 cannot be used on the boot partition

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In windoze yes, elsewhere yes (mostly) then no (no drive letters no boot problems)..

But I like those links, though Tom has a penchant for making the facts fit his view, now who does that remind me of ...?

[Matridom]

[quote]Originally posted by confus-ed:
Err I get about 25 with a single 7200, ata 66 disk, what I meant was that I wasn't gonna get 50 (PCI bus).

Obviously shows what chipsets, memory, blah blah can make to any system.



In windoze yes, elsewhere yes (mostly) then no (no drive letters no boot problems)..

But I like those links, though Tom has a penchant for making the facts fit his view, now who does that remind me of ...?

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Uhm, PCI bus can do 133 meg/s, ATA 66 can do 66/sec.. the hardware can handle it....

Tom does skew his notes/benchmarks.. but when those numbers can be verified by other people/sites then they mean a lot more. My aray is giving me about 90-95% of the theoretical throughput, that's pretty good. Either way, i think we've covered the subject matter throughly enough

[confus-ed]

[quote]Originally posted by Matridom:
Uhm, PCI bus can do 133 meg/s, ATA 66 can do 66/sec.. the hardware can handle it....
...... Either way, i think we've covered the subject matter throughly enough

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Well indeed! But PCI Bus (2.1 compliant -32 bit) is only capable of 33 m/bs hence why the bloody hell have a HD faster than 66Mhz, but if you had 64 bit bus (PCI 2.2 -coming soon-64 bit!) then yes with 16 bit d-word transfers max through put is 132 meg/s....

Like I said it depends what you are measuring how, your figures are counting each 'part' (half ,two disks, third , three disks etc...) as data passed across the PCI Bus, your figures are for data written not what went through the PCI pipe...

Your array seems to be giving you about 110% of the theoretical max....

That's very good!

[Matridom]

[quote]Originally posted by confus-ed:


Well indeed! But PCI Bus (2.1 compliant -32 bit) is only capable of 33 m/bs hence why the bloody hell have a HD faster than 66Mhz, but if you had 64 bit bus (PCI 2.2 -coming soon-64 bit!) then yes with 16 bit d-word transfers max through put is 132 meg/s....

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Uhm, i did the math...
(32 bit PCI)
32/8*33.3*1,000,000/1,048,576=127.2 MBytes/second.
(64 bit PCI)
64/8*33.3*1,000,000/1,048,576=508.6 MBytes/second.

your numbers are a little off

[quote] Your array seems to be giving you about 110% of the theoretical max...

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uhm, last time i checked, 18*2 = 36

[confus-ed]

Okay guilty of being old & befuddled!! I was infact(when I looked..) refering to the original PCI specs which would have only been able to transfer 1 d-word(8 bits) at a time so for your sum /4.

Whilst checking I came accross a thing called PCI-x which Seems to have a theoretical speed of 1000+PCI-x

Now if you can get that to 110% of theorectical max that's really really good....

[Ruslan]

[quote]Originally posted by Matridom:

The main advantage to RAID (Redundant Array of Independant Disks) other than data security is the insane read and/or write speeds.

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LoL! I always thought, what RAID is Redundant Array of Inexpensive Disks... Gotta learnt something new...

Thank You very much for the link,though - I do have Promise Ultra 66 PCI card,and will try to convert it to FastTrack.

[confus-ed]

[quote]Originally posted by Ruslan:
LoL! I always thought, what RAID is Redundant Array of Inexpensive Disks... Gotta learnt something new...

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Not Lol at all Ruslan, that is one of the definitions, back when software raid was all there was this was how you provided either speed/ redundancy rather than relying on more expensive solutions....

I guess it still means that especially with IDE.

[Six Eyed Smily]

one other thing to remember with raid - it can be a complete b*tch to install windows on...