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Old Oct 2, 2005, 12:17 PM   #1
rickvanr
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PM G5 and RAID

Hello,

I've been thinking about setting up a RAID 0 on my PM. Do both drives have to be identical sizes, ie. 250GB + 250GB?

Does RAID put an extra strain on drives? Or are the chances of a drive failing just as likely as any other time?

Thanks
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Old Oct 2, 2005, 01:25 PM   #2
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The drives don;t have to be identicl - they have to be the same size -- although I have heard of people using, say, a 250 Gb drive and a 250 Gb partition on a 400 Gb drive.

I'm just not a fan of RAID 0 in desktop computing scenarios. The risk of failure rises greatly, because any error on either one of the drives destroys the data across both drives. Although the 'strain' on the drive itself is no more than normal use, the consequence of failure is much higher.

And the theoretical (benchmark) speeed improvement is only attained under heavy, non-random loads like capturing digital video or a multi-user server environment. The overhead of the RAID computation nullifies much of the speed gain for small, random files access (such as typical single user desktop use)

I think you get more speed for your money and less risk simply by dividing your data and your OS/Scratch disk space onto two separate spindles. If you can install more than 2 drives, separate out your Applications and your OS onto separate drives as well.

Thanks,
Trevor
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Old Oct 2, 2005, 01:52 PM   #3
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Thanks Trevor, but with RAID 0 it'll act as having 1 500GB drive as compared to 2 x 250GB right?
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Old Oct 2, 2005, 02:22 PM   #4
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Originally Posted by rickvanr
Thanks Trevor, but with RAID 0 it'll act as having 1 500GB drive as compared to 2 x 250GB right?

Yup
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Old Oct 2, 2005, 08:27 PM   #5
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Recommendations on what block size I should use? 16k, 32k, 64k, 128k, or 256k?
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Old Oct 3, 2005, 10:14 AM   #6
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Recommendations on what block size I should use? 16k, 32k, 64k, 128k, or 256k?
Essentially, the RAID blocks are what split up the data. So it will write 64k to drive 1 then the next 64k to drive 2, then the next 64k back to drive 1, etc.

All the servers I have seen default to 64k and I've never had an issue with performance. If you really want to test it, try one block size, run a benchmark, then change the block size. Keep in mind that changing the block size will cause loss of data.
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Old Oct 3, 2005, 10:26 AM   #7
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If you had a 2 x 250gb to equal 500gb raid setup then took one out and put it in a firewire enclosure what would the data look like or would it be unreadable?
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Old Oct 3, 2005, 10:31 AM   #8
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If you had a 2 x 250gb to equal 500gb raid setup then took one out and put it in a firewire enclosure what would the data look like or would it be unreadable?
Good question.

With hotplug SCSI drives, it is important to get the drives in the same order as they were removed, but I've never tried it with an external.

So in theory, as long as you could instruct the RAID controller, whether it be in OS X or a hardware type, it should be able to view the configuration and bring it up normally.

EDIT: I am referring to if you attempt to keep the RAID. If you were thinking about removing just one drive and using just that drive as a volume, you won't be able to see any data, because the data is striped across two or more drives.
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Old Oct 3, 2005, 11:01 AM   #9
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Originally Posted by rickvanr
Does RAID put an extra strain on drives? Or are the chances of a drive failing just as likely as any other time?
The chances of an individual drive failing are pretty much the same as if you had two drives running independently; however, the overall odds of losing your data are higher with a RAID 0 configuration, because each drive is dependent on the other.

If you're looking for a speed increase, you'd be better off buying a Western Digital 74GB Raptor for the second bay.
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Old Oct 3, 2005, 11:46 AM   #10
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Quote:
Originally Posted by Brize
The chances of an individual drive failing are pretty much the same as if you had two drives running independently; however, the overall odds of losing your data are higher with a RAID 0 configuration, because each drive is dependent on the other.

If you're looking for a speed increase, you'd be better off buying a Western Digital 74GB Raptor for the second bay.
I'm not looking for a speed increase, I used to use a PB primarily. The G5 is fast. I just hate having multiple drives and having to copy things from one drive to the next.
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Old Oct 3, 2005, 01:13 PM   #11
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I'm not looking for a speed increase, I used to use a PB primarily. The G5 is fast. I just hate having multiple drives and having to copy things from one drive to the next.
Ah, I see. Personally, I'd only use RAID 0 as a last resort - there are more efficient ways of storing data across multiple drives - but if you specifically dislike having multiple drives, I guess it's the way to go. Best of luck, whatever you decide.
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Old Oct 3, 2005, 01:46 PM   #12
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If you're not looking for speed or data security, why not use it in JBOD mode?

[JBOD = Just a Bunch of Disks]

This aggreates all the disks together into one big disk, and can be used with disks of different size - e.g. one 50GB and one 400GB to make a 450GB virtual disk.

That would answer your seeming need to have maximum storage space on a single virtual drive.

Problem then is i think you won't know which data is on which drive. If one drive fails or is removed, it could be the one with the vital files or part of the OS on it.

I think the above posters are right - simply put as much as you can on one disk so it is as full as possible, e.g. OS, long term apps, stuff that doesn't change round much.

Use the other disk for your large files that you're always moving around.

Keep copies of vital folders e.g. mail backup, essays you've written, personal stuff etc on both disks so that if one goes, you've lost nothing irreplaceable.

xoxo

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