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When is software raid faster than hardware raid?

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June 17, 2011 5:36:06 PM

Hello,
under what circumstances is software raid more desirable than hardware raid? when is software raid faster than hardware raid?
a c 95 G Storage
June 17, 2011 6:37:03 PM

I think a software RAID is really only desirable when you cannot afford hardware RAID.

Software RAID Controller with 4 ports is about $50 where by a Hardware RAID Controller will cost you about $400.

http://en.wikipedia.org/wiki/RAID#Software-based_RAID
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a b G Storage
June 17, 2011 6:40:08 PM

Hardware RAID offloads the calculations (especially important in parity RAID such as 5/6/50/60) from the main CPU. Hardware RAID controllers also offer advantages such as caching etc. Hardware RAID is the way to go for enterprise class solutions but for a workstation/home PC you might be better off investing in more disks and doing software RAID 10.
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June 18, 2011 9:35:32 PM

Dont most motherboards support hardware RAID anyway? Why downgrade to software.
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a b G Storage
June 19, 2011 4:50:55 AM

No most motherboards have software RAID. In this case software RAID is referring to the calculations being done by the main CPU rather than a dedicated chip and memory on a RAID controller for XOR calcs. This is the type of RAID controller most enterprise storage solutions use as opposed to the $10 chip on most motherboards. If you aren't using a parity RAID (5/6/50/60) then this becomes much less important.
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a c 415 G Storage
June 19, 2011 6:21:17 PM

IMHO there really isn't anything fundamentally wrong with software RAID. Rumours of its excessive CPU requirements are greatly exaggerated, in fact no more CPU time is required for software RAID 0, 1 or 0+1. Even for RAID 5 the parity calculations are trivial for modern CPUs and are only required for writing or if you've lost a drive.

Software RAID is generally just as fast if not faster than hardware RAID because it eliminates protocol transfers between the Windows driver stack and the RAID card and it's firmware. It's a pretty trivial difference, but it's there. On the other hand hardware RAID often makes up for this through the use of large RAM caches to reduce I/O latency, especially for RAID-5.

The biggest downsides to software RAID are:

- software RAID generally only supports RAID 0 / 1 / 1+0 and 5. RAID-6, which is preferable to RAID-5 for the larger volumes being used these days is generally only supported by hardware RAID controllers.

- you're limited to the number of ports available on the motherboard controller (you can buy hardware RAID cards with many more ports).

- it's generally difficult to transfer drives between systems unless you can find another system with the same chipset & drivers (whereas RAID cards can be moved to a different system along with the drives).

- if your system hangs or crashes then the RAID volume might be left in an inconsistent state. (The same can happen for hardware RAID in the case of a power failure, but they're pretty much immune from software issues. And the better hardware RAID cards have battery-backed RAM to eliminate even power failures as a problem).
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a b G Storage
June 20, 2011 1:37:39 AM

I'm not sure I agree with sminlal here, a good hardware RAID controller would be significantly faster than software RAID simply because of caching. I think if you did a performance test between software RAID and a high end enterprise class controller with 512MB of cache you will see a difference.
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a c 415 G Storage
June 20, 2011 2:52:59 AM

As I said, "On the other hand hardware RAID often makes up for this through the use of large RAM caches to reduce I/O latency, especially for RAID-5."

That can make a big difference under certain circumstances for RAID-5 by eliminating a lot of the I/O operations required for updating the parity blocks. But for the other RAID organizations caching isn't such a big win because Windows itself caches data in system RAM, and these days most systems have a lot more system RAM available for caching than the RAID controller will.
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a b G Storage
June 20, 2011 3:20:29 AM

hence my "but for a workstation/home PC you might be better off investing in more disks and doing software RAID 10." (:
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a b G Storage
June 21, 2011 3:32:07 AM

rajive said:
Hello,
under what circumstances is software raid more desirable than hardware raid? when is software raid faster than hardware raid?


When you have at least duo core, and the raid does not requires lots of IO like files/web/database server or VMWare then you can use software raid

I only see the RAID0 ore RAID10, in some setup software raid is faster the hardware raid

If you look in this forum, there are hardware raid cost about $100.00
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a b G Storage
June 21, 2011 3:18:52 PM

It all depends on your controller. How much cache do you have? A GOOD hardware raid controller is more than $100. I'm sure you can find some crappy hardware raid controller that performs worse than software raid in some scenarios, but on average hardware raid is faster, and significantly so if you're using a partity RAID.
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a b G Storage
June 21, 2011 10:09:49 PM

A hardware raid offers these features:
- Rebuilt raid @ 250GB/hr
- Email notification of events, reports, SMART parameters, raid status
- Support RAID0/1/3/5/10 regard-less OS
- Managing RAID via GUI or hardware switches
- Support HDD greater than 2TB
- Up to five drives
- RAID5 transfer rate greater than 230MB/sec
- Firmware update-able
- About $119.00
- In the market about 2yrs
Would you call this a decent raid controller?

About the cache, it's a double edges sword. Use it w/o UPS is very good chances of data corruption
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a b G Storage
June 21, 2011 10:23:19 PM

Not really... a real enterprise class hardware RAID controller would usually support more than 5 drives and modern ones support RAID 50/6/60 It will come with 256MB/512MB or more of cache as well as an onboard battery backup for the cache on the controller in case of a power failure. Not having cache makes a significant performance difference.

Does that controller have a dedicated processor? If not you may just be paying for some decent firmware on a board and still utilizing your CPU for XOR calcs for parity RAID
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a b G Storage
June 21, 2011 10:27:49 PM

I would consider this a good hardware RAID controller.

Features
Sixteen internal + four external 6Gb/s SATA+SAS ports
Four internal mini-SAS SFF-8087 x4 connectors
One mini-SAS SFF-8088 external connector
6Gb/s throughput per port
LSISAS2108 ROC
Half-Length, Full Height (6.6” x 4.376”)
x8 PCI Express 2.0 host interface
512MB DDRII cache (800MHz)
Optional battery backup unit (LSIiBBU07 or LSIiBBU08 remote mount with LSI00260)
Connect up to 240 SATA and/or SAS devices
RAID levels 0, 1, 5 and 6
RAID spans 10, 50 and 60
Auto-resume on rebuild
Auto-resume on reconstruction
Online Capacity Expansion (OCE)
Online RAID Level Migration (RLM)
SSD support with SSD Guard™
Global and dedicated hot spare with revertible hot spare support
o Automatic rebuild
o Enclosure affinity
o Emergency SATA hot spare for SAS arrays
Single controller multipathing
I/O load balancing
Comprehensive RAID management suite
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a b G Storage
June 21, 2011 11:35:59 PM

tokencode said:
Not really... a real enterprise class hardware RAID controller would usually support more than 5 drives and modern ones support RAID 50/6/60 It will come with 256MB/512MB or more of cache as well as an onboard battery backup for the cache on the controller in case of a power failure. Not having cache makes a significant performance difference.

Does that controller have a dedicated processor? If not you may just be paying for some decent firmware on a board and still utilizing your CPU for XOR calcs for parity RAID


Who is in the right mind would use such costly controller for SOHO and media server?! That is such a waste of money
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a b G Storage
June 23, 2011 1:33:06 AM

FireWire2 said:
Who is in the right mind would use such costly controller for SOHO and media server?! That is such a waste of money



I was not suggesting this for a SOHO build, media server that all depends on what your serving and how many. What I was saying is that a true hardware RAID controller has a processor and dedicated cache, otherwise it's really software on a chip just like is included on most motherboards. The controller you listed I do not believe is a hardware RAID controller. The calculations for parity would still be done by the system CPU, not a dedicated processor. The thread started by asking which was faster, I stated hardare RAID, you said software in some cases and I disagree. If you use a real hardware RAID controller, it will always be faster, given the same generation of technology if for no other reason than the cache.
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a b G Storage
June 23, 2011 6:34:36 PM

Quote:
The controller you listed I do not believe is a hardware RAID controller. The calculations for parity would still be done by the system CPU, not a dedicated processor...


Don't just believe! Get fact before comment!
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a b G Storage
June 24, 2011 8:59:08 PM

Thats hard to do when you don't include a model number..... and I staqnd by my comment that the controller you listed is not a good hardware RAID controller...
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a b G Storage
June 24, 2011 9:03:53 PM

What is the model number? If you have souething does that parity calcs for $100, thats good deal.
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a b G Storage
June 24, 2011 9:52:54 PM

tokencode said:
Thats hard to do when you don't include a model number..... and I staqnd by my comment that the controller you listed is not a good hardware RAID controller...


Understand

Here is it SPM393

Here is the product chip-set brief

One user uses and gives it five stars, although I would give it another 5 stars
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a b G Storage
June 24, 2011 10:20:01 PM

Interesting, it actually does have a dedicated processor and cache, it doesn't say how much buit thats still impressive. I'm guessing the cache is non-volitle since there is no battery I can see... It almost looks like a Cisco WIC.

http://www.ioisata.com/products/Port-Multiplier/SPM393....

I wouldn't use it in a enterprise server per say but that is an interesting and cost effect option for a SOHO solution. I would that this controller would be faster than software RAID/"firmware" RAID.
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a b G Storage
June 24, 2011 10:47:28 PM

tokencode said:
Interesting, it actually does have a dedicated processor and cache, it doesn't say how much buit thats still impressive. I'm guessing the cache is non-volitle since there is no battery I can see... It almost looks like a Cisco WIC.

http://www.ioisata.com/products/Port-Multiplier/SPM393....

I wouldn't use it in a enterprise server per say but that is an interesting and cost effect option for a SOHO solution. I would that this controller would be faster than software RAID/"firmware" RAID.


I would not use for enterprise either, but it would be a nice back-up for the main server.

It has an impressive random read transfer rate. Perfect for Media Server
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a b G Storage
June 27, 2011 5:14:01 AM

So if I understand it correctly, it just piggybacks off of an internal SATA controller. Does that mean it's limited to the through put of a single SATA port? Not that it matters all that much with SATA III
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a b G Storage
June 27, 2011 7:44:12 PM

Yeap, just connect it internal SATA, there is NO driver required

I have use this controller with FreeNAS, Window7, MAC OS 10.6.7, OpenFiler, SAMBA... via internal SATA connection

MAC OS 10.6.x - For HD video editing via Final Cut speed range from 210MB/s to 245MB/sec (mac pro has 2x SATA connectors behind the fan, hidden from the straight view)

Window7 - same speed, but the interesting is internal SATA 3 host would give 10 ~ 20% higher speed from SATAII

Where FreeNAS, Openfiler, and SAMBA you should get MAX transfer rate from it Gb network
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June 28, 2011 12:47:42 AM

Get an Adaptec RAID 2805 for 275 dollars. It's more than a software controller but IMO the price is quite nice for what you get. Ideally it's for a workstation or small server.
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a b G Storage
June 28, 2011 1:03:10 AM

The nice thing about FireWire's controller which is also hardware RAID is that it's transparent to the OS, no drivers needed. Your adaptec is more long the lines of what I was thinking of as well, but Firewire's solution is very interesting and 1/2 the price the of the adaptec.
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