Why is Raid0 faster?

Zulu

Hi Folks,
I'm looking at buying a new pc (as some of you might know already), and I'm trying to understand why a 10000 hard disk would be faster in a Raid0 setup?

I understand the concept of Raid, but why would that be any faster at retrieving info than otherwise? Can anyone explain please?

Cheers

10-10-20

Because the seek-times for the drive head causes a delay on a single disk, but with two disks, you can send out the access request sequentially and the two disks will go off to perform the operation independently, returning the data quicker.

Zulu

Ah, so would I be right in say then that as one controler seeks a packet, the other one seeks the next required packet?

Anti

1. go to wikipedia.com
2. type in raid0

That will give you the best possible description. Did you even think of doing your own research before asking here ?

10-10-20

Yes, you then remove the latency associated with the head-seek through this method. lookup "NCQ" for some similar functionality.

10-10-20

Anti wrote: »

1. go to wikipedia.com
2. type in raid0

That will give you the best possible description. Did you even think of doing your own research before asking here ?

Jesus - I don't think that's the spirit.

Zulu

Anti wrote: »

1. go to wikipedia.com
2. type in raid0

That will give you the best possible description. Did you even think of doing your own research before asking here ?

3. don't bother posting if it bothers you so much.

FYI: I went to wiki and read the article. It didn't explain why a 10000 hard disk would run faster. I then did a short search in google, instead of spending 2 hours, I came to boards to ask a helpful person.

Thanks a million 10-10-20.

Khannie

Anti wrote: »

Did you even think of doing your own research before asking here ?

Take it easy please.

steve-hosting36

10k rpm basically means the disk will physicall spin faster than a normal drive (at 5400 or 7200rpm). Faster spinning means faster data reading and writing. (Server drives can spin at up to 15k rpm).

Raid 0 means read/writing to and from two disks at the same time, so you essentially get 'similar' performance to a 20k rpm drive (in simple terms).

Zulu

Ah yea I get that, but I was reading reviews about the 10000 disks and a common theme was in RAID0 it was espically fast.
I was just trying to understand how it could be that much better.

Thanks for the replies.

ZygOte

Anti wrote: »

1. go to wikipedia.com
2. type in raid0

That will give you the best possible description. Did you even think of doing your own research before asking here ?

ooooohhhhh handbags......

irlrobins

ZygOte wrote: »

ooooohhhhh handbags......

Move on people. *taps infraction stick*

Anti

Sorry if i came across bitchy in my above post. It wasnt meant that way, but i find it really annoying when someone hasnt a clue why somehting works the way it does without even trying to find out them selfs.

RoyalMarine

Anti wrote: »

Sorry if i came across bitchy in my above post. It wasnt meant that way, but i find it really annoying when someone hasnt a clue why somehting works the way it does without even trying to find out them selfs.

but it gets the rest of us thinking and talking about it. and other people who dont know are drawn to the forum to read more.

Anti

RoyalMarineComm wrote: »

but it gets the rest of us thinking and talking about it. and other people who dont know are drawn to the forum to read more.

Thanks what they want you to think !! Its all part of the lizards people's plan !!

irlrobins

Again I say it, get back on topic.

L31mr0d

A good example about RAID 0 I just made up:

Imagine you went into McD's and there was only 1 till open with 10 people waiting for their delicious Beef Deluxe With Bacon. You'd be pissed at having to wait right. The smart thing to do to speed things up would be to open another till and split the queue in half, this is effectively what a RAID 0 is, it gives another lane for traffic to move in.

BUT, there is a caveat, say McD's can only make 1 Beef Deluxe With Bacon at a time, splitting the queue in half will make no difference to how long people will have to wait. This is the issue you will have with the RAID controller on your motherboard. It is very possible to bottleneck the integrated software RAID controller on the motherboard (something I'm having problems with atm)

The way to get around this problem is to buy yourself a hardware RAID controller, but in fairness, if you are willing to fork out for HW RAID controller you might as well just save yourself the headache and buy yourself a SSD (the Subway of the HDD world)

Now... where to go for lunch today?

10-10-20

I just wanted to clear off one final point - a 10k (10,000 RPM) disk will have a Rotational Latency less than that of a 5400 or 7200 RPM disk.
Rotational Latency is the time in miliseconds to which a full rotation of the platter occurs. At 10k, this is 0.1 miliseconds (.0001 of a second) and at 5400 this is .185mS.
In a worst-case scenario where the reads are not sequential or it overlaps the boundry of a 360 degree rotation of the platter, the head will be forced to wait an additional time period for the platter to rotate around again before the data becomes available to it.

Hence, gains are seen when the platter is spinning faster...

DanGerMus

Zulu wrote: »

I understand the concept of Raid, but why would that be any faster at retrieving info than otherwise? Can anyone explain please?

Cheers

You may well understand one of the concepts of raid. But there are 10 (i think) differant kinds. Most are to do with redundancy. Where as raid0 is purely a performance setup.

Check out www.raid.com and click on the raid.edu tab and it explains all the dfferant kinds of raid very well. Thats where i learned about it.

I might be off the mark. But i had an experience with my brother once who is now a network admin where i was tellin him about how i was putting raid on my pc for extra performance. He looked at me as though i had just grown an extra head right before his eyes. When i proceeded to explain why i was using raid he stopped me and said "i know what raid is" (in a tone that meant i dont need YOU to tell me) which to be fair he didnt need me to tell him about raid as it partains to redundant storage systems. But as a person working with networks his primary experiences had nothin to do with speed/performance as such, more reliability. Any way to wrap it up i eventually explained it and he got got it. The point is there is more than one application of raid type systems.

Zulu

Funny you should say that! My brother had the exact same reaction, and is also a n/w admin
My limited knowledge was from a reliability pov. Thanks a million for the link, I'll have a read.

L31mr0d

DanGerMus wrote: »

Any way to wrap it up i eventually explained it and he got got it. The point is there is more than one application of raid type systems.

This is true, the actual term "RAID 0" is a misnomer as it offers no redundancy at all.

10-10-20

Ever hear of RAID 69?

Once one drive goes down, they all go down...

Zulu

hey folks,
well I got the new machine, and now I'm trying to work out how to configure RAID0 arcoss my disks. (I got a nForce 680i SLI mainboard)
So far I went into the Bios and turned RAID on, and set the first 2 sata "0" drives (master and slave) on.
It booted in about 2 seconds, but it can't have been that easy? Can it? (And I would have expected to have to reinstall os etc?) Can anyone clarify for me please?

THanks

Stephen

What OS? If its Vista it probably has drivers for your raid controller built in.

Zulu

sorry yea it's vista. But in explorer i still see 2x150GB drives - I was expecting 1x200GB (2 drives appearing as one raid, and loosing 1/3 of the space?)

MAJJ

Hi Zulu,

Of the 2 drives you have what are the sizes of each? I reckon your going to say that the smallest is 150GB? If you use drives of different sizes, you won't be able to access the larger drive's extra room. In other words, a 120GB drive paired with an 80GB unit in a RAID 0 will look like 160GB (two 80GB drives) to the PC.

Quoted from here - http://www.smartcomputing.com/Editorial/article.asp?article=articles/2004/w1510/11w02/11w02.asp&guid


Also, I assume you know you will have no redundancy/fault tolerance?

majj

sebastianlieken

10-10-20 wrote: »

At 10k, this is 0.1 miliseconds (.0001 of a second) and at 5400 this is .185mS

wait wait wait...hold the phone. you mean to tell me that i can speed my hard drive up by 0.085 whole mili-seconds!....:eek:

Zulu

MAJJ wrote: »

Hi Zulu,
Of the 2 drives you have what are the sizes of each?

Hi MAJJ I've 2 x 150 (same drives)

Also, I assume you know you will have no redundancy/fault tolerance?
majj

yup i know

PogMoThoin

Set Sata mode to raid in the bios.
Press ctrl and I to get in2 the raid utility during bootup when prompted.
Create the raid partion.
Vista will then see it as a single drive during install.

Dorsanty

Hmmm, so far no one has said raid0 has some read access performance issues. So lets begin,

raid0 is striping and there are situations where accessing the raid0 volume is no better then having a single real hard disk. Read http://en.wikipedia.org/wiki/RAID_0#RAID_0 in the performance section. It suggests that reading large files creates this situation of performance == to single disk. Hmmm, do games have any large files to be loaded.

raid1 is mirroring and here you have to sacrifise any increase in space but what you get in return is the read performance. because the data will be present on each disk when a file is read the various blocks can be read from either disk allowing an increase in read speed equal to the number of disks in the mirror (no doubt bottlenecked by your controller at some point). So when you want stuff to load faster raid1 is the man.

So while raid0 does improve write performance, the read performance in certain situations can be just equal to the single physical disk. raid1 means you don't get to double your storage and your write performance is only equal to single disk but your read speed is the dogs.

So question is what do we want most, to write as high speed or to read? I personally think a gaming rig requires a raid1 setup for accessing the game files.

Of course you can do raid 0+1 or raid 10 to get the best of both worlds but I'm assuming home users don't have the cash for that.

Capt'n Midnight

10-10-20 wrote: »

Ever hear of RAID 69?

Once one drive goes down, they all go down...

LOL

Stripe size is important too. Lets say you have a stripe of 64KB. Then most of the time when you save a small file less than 64KB it will be stored on just one disk. So the drive will be able to handle two at the same time. Files larger than 64KB will be spread across both disks so you get twice the bandwidth when copying them.

Another option is to look at drives with flash memory or ram cards can act as drives. these will act as a cache and will speed up data accessed repeadly but won't do anything for say video recording that is larger that teh cache. Memory is called RAM because it's random access in the sense that you don't have to wait.


You should be able to speed up seek times by using small partitions on a large drive. This would also speed up data transfer rates too. eg: replacing a 7200 20GB drive with a 200GB one and setting up a 20GB partition on it.

In an ideal world you could have multiple drives with spindles synchronised. All drives would store the same info. If you had 3 drives then you could have them 120 degrees apart so you would only have to wait 1/3rd of the time before the wanted sector came round. It should be possible to get each drive then to feed back 1/3rd of the data to increase throughput. Writing would be tricky as you would have to write to each drive. Probably not possible since drives would have their own cache on them anyway.


Overall would RAID 0 be any faster than putting the OS, Swap file and Data on separate drives. If doing work where you are processing large files have the file read from one drive and written to another is much faster than writing back to the same drive even with RAID and you are far less likely to get fragmentation either.

stereo_steve

Anti wrote: »

1. go to wikipedia.com
2. type in raid0

That will give you the best possible description. Did you even think of doing your own research before asking here ?

Couldn't agree more. I used to come to this board alot but I don't anymore. There is too many stupid threads that are created out of sheer lazyness by people. Its a shame when I remember what it used to be like two years ago.

Zulu

stereo_steve wrote: »

Couldn't agree more. I used to come to this board alot but I don't anymore. There is too many stupid threads that are created out of sheer lazyness by people. Its a shame when I remember what it used to be like two years ago.

...we'd probably have a hell of a lot less crap to wade through if people 1) bothered to read the thread first and 2) didn't post innane crap. :rolleyes:

irlrobins

Right, last warning. Next comment that isn't answering the OP or otherwise unrelated gets a ban.

10-10-20

I heard mention of spindle-sync (with the little sync cables and all!).

Spindle-snyc hasn't been used since the availability of on-drive cache, T/NCQ and the better sustained transfer rates of 80MB/sec (only on the bus) with SCSI-2.

wait wait wait...hold the phone. you mean to tell me that i can speed my hard drive up by 0.085 whole mili-seconds!....

You do >500 IO operations per second, and you'll appreciate '0.085 whole mili-seconds'.

Capt'n Midnight

10-10-20 wrote: »

I heard mention of spindle-sync (with the little sync cables and all!).

my proposal would be technically possible but not practical and it would only improve latency. seek time would be the same. writing speed wouldn't be improved

GO-RAMDiSK-BOX is another option, pricey and small but very fast, no seek or latency overhead but you'd need a rock solid way of backing it up regularly.