RAID 5 question - 2 x 320 + 1 x 500?

Participant

Participant

Participant

Caporegime
Joined
13 May 2003
Posts
34,510
Location
Warwickshire
Ok I have a RAID question and would appreciate it if someone could clear it up for me.

I'm getting the Gigabyte DS3P and want to use the following storage configuration with an aim to achieve RAID 0 speeds with redundancy:

2 x 320Gb Seagate 7200.10 + 1 x 500Gb WDYS or KS

I'd want to set up the two Seagates in RAID 0 but protect the data with mirroring on the Western Dig.

Two questions:

- Does RAID 5 support two different hard drives and capacities
- Does the DS3P do an effective job of RAID apart from RAID 0 and RAID 1 or will I require a seperate controller card to do this effectively?

Many thanks.
 
RAID5 will support mismatched drives but it's not the best idea. You'll end up with an array which is (for 3 drives) twice the size of the smallest drive and unless your using an Intel Matrix RAID controller the unused space on the other drives will be unaccessible.

The DS3 only supports RAID0 or 1 because it can only support 2 drives in RAID using the JMicron controller - the Intel southbridge is the non RAID version and while it supports a further 4 disks they can only be configured as single drives.

You could go RAID5 with an add in card but the DS3 only has PCI or PCIe 1x slots once you put a graphics card in so you'll be limited to software or accelerated software based RAID cards like the Highpoint RocketRAIDs. These are fine for storage but the write speed is too low to realistically use as a main drive, task swapping would be painful.

The best option could be to go with RAID0 on the DS3 with a pair of 320s and then have a 500 as a separate disk and use the Synctoy powertoy or something similar to backup critical files and folders from the array to the 500.
 
It is also wirth noting that RAID 5, even when setup correctly with proper RAID controllers (I personally don't think RAID 5 should be considered on any of the low end controllers available), read speed will always be good but write speed always suffers.
This is due to parity being written across all of the disks and file servers (where RAID 5 is usually found) spend a lot more time dealing with read requests than they do with write requests.

RAID 5 really isn't the best option for home use.
 
Ok thanks for the replies guys. It sounds like 2 x 320 in RAID 0 + 1 x 500 storage is good advice.

RAID 5 confuses me though. How can you have redundancy plus striping when you only have three disks of the same capacity? E.g. x = size of one disk, 2x = size of striping array, therefore you can only ever back up half of your striped data?? Obviously this is wrong but would be grateful if you could put me right.
 
Robbie G said:
RAID 5 confuses me though. How can you have redundancy plus striping when you only have three disks of the same capacity? E.g. x = size of one disk, 2x = size of striping array, therefore you can only ever back up half of your striped data?? Obviously this is wrong but would be grateful if you could put me right.
Click to expand...
RAID5 doesn't store a complete second copy, only enough parity data to reconstruct the data from one disk.

The parity bits are the XOR of all the data bits for each block of the array, to reconstruct the data the parity is XOR'd again with all the remaining data bits to generate the missing data. For example for data blocks A & B the parity is shown below:
Code: 
A     B    Parity
0 XOR 0  = 0
1  "  0  = 1
0  "  1  = 1
1  "  1  = 0

Now if block A is lost due to hardware failure it can be recalculated:
Code: 
B     Parity   A
0 XOR 0      = 0
0  "  1      = 1
1  "  1      = 0
1  "  0      = 1

The same principle holds regardless of how many disks are in the array and better still the one parity block can be used to regenerate the data regardless of which data block is missing.
 
Gotcha, thanks for that. RAID is a science in itself!

I'm also thinking about saving a bit of cash by buying a couple of SATA converters and using my current two WD 120Gb IDE drives instead of a new SATA for specific daily scheduled backups to run overnight, but I'm worried about two things:

- will the IDE drives slow down the rest of the system in any way (apart from obviously when running the backup)
- do drives generally make any noise at idle as I want this to be a really quiet system

Many thanks.

EDIT - if I go down the above route then could I not also set up the IDE drives in RAID 0 for increased backup speed? Granted this is riskier but I'd be v unlucky if both RAID arrays failed! The only problem with this is - does the DS3 support RAID for IDE drives on SATA channels?
 
Last edited:
Robbie G said:
- will the IDE drives slow down the rest of the system in any way (apart from obviously when running the backup)
Click to expand...
No, they'll run independently.
Robbie G said:
- do drives generally make any noise at idle as I want this to be a really quiet system
Click to expand...
The drive continues to spin when idle so there will be some noise, the level of which is dependant on the type and quality of the bearings used. You could set the power options to spin them down after a set amount of inactivity however if you only want them for backups then think about external caddies. That will allow you to control when they're powered on and by having them off when they're not needed protects them from power spikes etc.
 
Ahha of course! Windows has an HDD power down facility. That's my answer then. Finally - any idea on my IDE / RAID question? Sorry for asking lots of questions of you, but this has been very helpful and it's my last question, promise!
 
Robbie G said:
EDIT - if I go down the above route then could I not also set up the IDE drives in RAID 0 for increased backup speed? Granted this is riskier but I'd be v unlucky if both RAID arrays failed! The only problem with this is - does the DS3 support RAID for IDE drives on SATA channels?
Click to expand...
While it would be unlikely that both arrays failed at once the point of a backup is that it's safe, speed is a secondary concern and hence RAID0 is a bad idea for backups. Unless your making a crazy amount of changes to the data incremental backups should be pretty quick anyway.

Mind you the DS3 only supports a single 2 disk RAID array so this is all a moot point.
 
You must log in or register to reply here.
Back
Top Bottom