Software Raid and CPU usage

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Level 1

1 points

Software Raid and CPU usage

Hello everyone
I searched through the forum carefully but didnt find anything that closely represented my question.
If I understand correctly the only ways to get RAID on a system is to use hardware RAID (either planted on Mainboard or PCI/PCI-E cards) or to use software RAID offered by Mac OSX.
I recetnly purchased two drives in order to run them as RAID 0 setup to increase my speed.
Heres my question : How good is Software RAID performance? will it hog my CPUa alot since its software based? Although hardware dedicated RAID always performs better but how good is the performance from the RAID option in Mac OSX?
I thank you in advance for your time and help

Mac Pro 2.66, 2GB, 160GB HDD, 80GB HDD, 7300GT, Bluetooth, Mac OS X (10.4.6), P4 2.6C w/ HT, 1GB Dual channel DDR400, 200GB HDD, Radeon X850XT, Audigy 2

Posted on Apr 6, 2007 10:31 PM

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Answer 1

Apr 6, 2007 11:00 PM in response to DaTaNa

I have 4 250GB drives in my Pro set in a stripped raid. Watching my processors, I don't see any negative impact on them.

If I'm not mistaken (please correct me if I'm wrong), it's either the EFI firmware or the SMC firmware that initializes the raid upon boot up. So the raid is the close to the first thing that is started.

Yes, it is a software raid, but separate from the OS itself in a manner of speaking.

Sam

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Answer 2

Apr 7, 2007 11:52 AM in response to DaTaNa

Software RAID 0 and RAID 1 have very little CPU impact -- there is no real calculation that must be done -- the OS just writes or reads across multiple drives.

RAID 3 or RAID 5 are where you want hardware RAID, because every write must generate parity information which allows the system to calculate values that "aren't there" in the case that a disk fails.

RAID 0 will be faster than a single disk. Of course, it is slightly more than twice as likely that you will lose data -- so have a good backup plan.

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Answer 3

DaTaNa Author

Level 1

1 points

Apr 7, 2007 12:47 PM in response to DaTaNa

Thank you all
I'm going to proceed with my RAID 0 plan and as you have suggested, I have dedciated an internal and external drive to do my backups.
Thank you

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Answer 4

Apr 7, 2007 12:56 PM in response to William Lloyd

Yup. The OS is just talking to the same controllers. The
only thing that's changed AFAIK is the organization of the
controller requests if you will. It's still not as fast as
a hardware RAID 0 solution for the obvious reasons such as
dedicated high-speed I/O cache and optimized controllers
and etc. A GREAT hardware RAID 0 gets about twice the speed
as our software RAID 0 - but with a 3drive RAID 0 we're
just about (or a little over) twice what we get from a
single fast HDD.

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Answer 5

DaTaNa Author

Level 1

1 points

Apr 7, 2007 4:14 PM in response to DaTaNa

I also have a 160GB drive that came standard with my MP. is it possible to buy another 160GB drive and use it as RAID 0? Or both drives MUST be identical?
Thank you for your help

I have some questions regarding how I can use two HDDs. I want to ask if it is possible to pair two different yet same size drives as RAID 0

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Answer 6

DaTaNa Author

Level 1

1 points

Apr 7, 2007 4:14 PM in response to DaTaNa

edited.

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Answer 7

Apr 7, 2007 5:29 PM in response to DaTaNa

I also have a 160GB drive that came standard with my
MP. is it possible to buy another 160GB drive and use
it as RAID 0? Or both drives MUST be identical?

The drives used /should/ have identical geometry but I
have seen software RAIDs where it wasn't the case. That
said you should be able to find the same part that Apple
used for the original.

I and a few other here, will recommend the Maxtor MaxLineIII
drives for their exceptional performance and uber low price
point. Basically $75 for 300 gigs. Get 3 of those and keep
the 160 as a system backup or as a dedicated boot drive.

Thank you for your help

I have some questions regarding how I can use two
HDDs. I want to ask if it is possible to pair two
different yet same size drives as RAID 0

Sometimes yes, sometimes no - but not recommended.

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Answer 8

The hatter

Level 9

61,031 points

Apr 8, 2007 7:54 AM in response to Tesselator

Apple used the 7200.9 and I would not want to install another - even with no data and just sitting there it reports hotter temps. With it used in a RAID with another brand of 160GB drives it caused problems. . .

I would never endorse mixing drives, mixing firmware or revision.

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Answer 9

Apr 8, 2007 3:14 PM in response to The hatter

Agreed. The drive (drives?) they offer with the standard kit
reflects a really poor choice in parts. I guess it was one
of those internal handshakes (bulk undesirables for next to
nothing).

But hey, you actually tried to use that drive in a RAID? 🙂
You say there was trouble... What happened exactly? I'd be
interested to hear about it if you have the time.

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Answer 10

el Duque

Level 1

135 points

Apr 8, 2007 3:58 PM in response to Tesselator

That's why i'm using that drive (stock) as my windows vista drive. If it fails, oh well!

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