Why is RAID fast?

Guest2 · 21 Sep 2009 at 11:19

I dont really understand raid but know that its good for if a drive dies, as the other will just take over. What makes raid faster than running a single drive?

I would have thought that raid would be slower as both drives are reading/writing data at the same time

Is there any point in setting up RAID (if its possible) on 2 500gb different model drives. Would i lose 500gb but gain speed and reliability, if one dies obviously

bledd · 21 Sep 2009 at 11:20

raid 0 is the 'fast' one

if you have a 100mb file, 50mb will be saved on one drive, 50mb on the other

so each drive only has to read 50mb each, meaning you read the file in half the time.

that's the basics of it

this calculator will tell you the basics too..

http://www.ibeast.com/content/tools/RaidCalc/RaidCalc.asp

1
0
10 (or 0+1 , 1+0) etc
5

are the commonly used types

Ev0 · 21 Sep 2009 at 11:22

Yup different types of RAID for different purposes/applications

Guest2 · 21 Sep 2009 at 11:22

So if one of the drives die then you lose one half of the file? Surely not

I think at work our file server has 8 drives in raid where the data is 'striped' accross them? If one dies does it just shift the data to the others before?

Paul11 · 21 Sep 2009 at 11:23

Guest2 said:
So if one of the drives die then you lose one half of the file? Surely not

if one drive dies, you lose all the data on both drives

Guest2 · 21 Sep 2009 at 11:26

Paul11 said:
if one drive dies, you lose all the data on both drives

a bit risky isnt it? We must be using a different type of raid. One of our disks died a few weeks ago and it was replaced and everything went on as normal

Paul11 · 21 Sep 2009 at 11:27

Guest2 said:
a bit risky isnt it? We must be using a different type of raid. One of our disks died a few weeks ago and it was replaced and everything went on as normal

raid 1 is different to raid 0 but has no speed advantages

raid 1 is for copying data from one drive to another

yes, it is more risky having a raid0 but just highlites the need for good backups

you should always have more than one copy of your data no matter what type of drive system you are using

Guest2 · 21 Sep 2009 at 11:37

Thanks. Think ill stick with a velociraptor (when it arrives) as my primary, 2 500gb drives for storage and a 250gb drive for backing up the velociraptor every few weeks
(and a 1tb external for backup)

Stonedofmoo · 21 Sep 2009 at 11:41

Paul11 said:
raid 1 is different to raid 0 but has no speed advantages

Yes it does. It gains a read increase because the OS is able to read the existing files off both disks at the same time. But it gains nothing on writing as obviously both drives are writing exactly the same thing

paradigm · 21 Sep 2009 at 11:54

Guest2 said:
a bit risky isnt it? We must be using a different type of raid. One of our disks died a few weeks ago and it was replaced and everything went on as normal

I would imagine that in a corporate environment, you'll be running something like RAID5, RAID6, RAID10, RAID50 or RAID60.

Both speed and redundancy advantages, without the risk of data loss for one (or more, depending on RAID level) drives.

Beerbaron · 21 Sep 2009 at 12:03

http://en.wikipedia.org/wiki/RAID

Guest2 · 21 Sep 2009 at 12:15

paradigm said:
I would imagine that in a corporate environment, you'll be running something like RAID5, RAID6, RAID10, RAID50 or RAID60.

Both speed and redundancy advantages, without the risk of data loss for one (or more, depending on RAID level) drives.

From my brief reading i thought there was only raid 0 (writes 50/50, faster but data loss on both),1 (writes accross all but lose disk space) and 5 (minimum 3 drives, can only lose one drive but a bit faster)

Ill look into raid 6, 10, 50 and 60...

edit - reading this http://en.wikipedia.org/wiki/Nested_RAID_levels#RAID_60_.28RAID_6.2B0.29
looks like we are using raid 60

bledd · 21 Sep 2009 at 12:23

you'll be likely using raid5 in work

data is striped across many drives

http://en.wikipedia.org/wiki/RAID

Guest2 · 21 Sep 2009 at 12:25

bledd. said:
you'll be likely using raid5 in work

data is striped across many drives

http://en.wikipedia.org/wiki/RAID

I thought only one drive can fail though in raid5. Im sure my boss said 2 can fail

(from raid 60 on wiki) any two drives can fail without data loss and up to four total as long as it is only two from each RAID6 sub-array.

Stonedofmoo · 21 Sep 2009 at 12:29

Basically you require dedicated hardware cards for the other types of RAID. On home setups you only see RAID 0/1/5

Paul11 · 21 Sep 2009 at 12:34

Stonedofmoo said:
Yes it does. It gains a read increase because the OS is able to read the existing files off both disks at the same time. But it gains nothing on writing as obviously both drives are writing exactly the same thing

only if the controller supports split seeks

Guest2 · 21 Sep 2009 at 13:33

Stonedofmoo said:
Basically you require dedicated hardware cards for the other types of RAID. On home setups you only see RAID 0/1/5

Mate has got a hardware card that can do RAID 10. Doesnt it depend on what motherboard you have as to what types of raid can be done?

Think my S939 DFI ultra-D board can do raid 0 and 1, not sure about 5

AbsenceJam · 21 Sep 2009 at 14:01

Guest2 said:
Mate has got a hardware card that can do RAID 10. Doesnt it depend on what motherboard you have as to what types of raid can be done?

Think my S939 DFI ultra-D board can do raid 0 and 1, not sure about 5

Yes but mostly 0 and 1, sometimes 5. Alsom RAID 5 requires a lot of calculations so dedicated cards with XOR processors are very much faster than onboard RAID 5 which does this in software.

LeJosh · 21 Sep 2009 at 17:01

bledd. said:
you'll be likely using raid5 in work

data is striped across many drives

http://en.wikipedia.org/wiki/RAID

I thought RAID0 was for striping.

RAID5 uses parity data, storing enough data in all the drives so that if one fails you can hot swap the other and it will rebuild the data.

Example - if you have 4 drives (3 is minimum for RAID5) for simples sake it will be like.

1 0 1 0

one goes pop

1 0 x 0

will occur and the parity will recognise that it has to be a one in there because they have to be even. Off the top of my head that's what it is. So will go back to 1 0 1 0. I might just be drivvling on though.