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AHCI vs RAID


Harroguk
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 From what you posted, it seems like  Intel RAID is a subset, or added feature, of Intel AHCI. 

 

It is.  You turn on the Intel RAID, it still acts exactly the same as the AHCI until you set up an array.  You can also run an array and seperate drives without setting them up in a single drive array like the B120i.

 

The B120i seems to be controlled by the Intel chipset hardware, but with HP's firmware which pretty much gimps it.

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So which should I choose and why?

 

Assuming you really want to boot from SSD on the ODD sata port, my understanding (just from reading, not from experience) is that you dont have much choice, and you do have to set that drive to RAID 0.

 

And no, you dont "lose" anything in doing so.

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Agreed, best to set the drive to RAID0. An HP employee made a post to this effect quite some time ago. And, because the drive is in RAID mode on the B120i, you have a better chance at reduced fan speeds.

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This is the understanding I have come to. I just don't understand why anyone would ever choose AHCI?

 

Those who dont have a raid controller.

 

Or those who have but do not want to use it.

 

 

 

...

 

 

Now keep in mind RAID has its own purposes. You will use it if you absolutely need redundancy.

 

Also it comes in many flavors and types. Firmware Software, hardware, OS-level software (examples: drive pool, storage spaces, ZFS) or 3rd party Application level (drive bend , snap raid).

 

Btw, what i meant was:

 

It comes in many flavors and types. Firmware software, Hardware, OS-level software (examples: Drive Extender, Storage spaces, ZFS) or 3rd party Applications (Drive Pool, Drive Bend, Snap Raid).

Edited by doomed
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This is the understanding I have come to. I just don't understand why anyone would ever choose AHCI?

 

Another reason not to use the raid controller, is if you want to have the disks as plain as possible. Let's say to be able to take them out and connect directly in a another computer, in any given situation. 

I assume it would be easier to be able to read the disk on a standard desktop computer if the disk is not in any RAID mode. Though i'm not sure if RAID-0 counts for anything in this case, so my assumption might be wrong.

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Another reason not to use the raid controller, is if you want to have the disks as plain as possible. Let's say to be able to take them out and connect directly in a another computer, in any given situation. 

I assume it would be easier to be able to read the disk on a standard desktop computer if the disk is not in any RAID mode. Though i'm not sure if RAID-0 counts for anything in this case, so my assumption might be wrong.

 

Yes! +1

 

A raid filesystem (such as ZFS) prefers drives to be passed transparently. There is a real trend for using LSI HBAs with the IT firmware (aka. passthrough).

 

...should your server pack up, simply move the drives to another machine and import the pool - heck, even move to another distribution/release if you want.

 

Overall if you are BSD (or even Linux) based, the benefits are huge. Not to mention incredibly cost effective.

 

Providing your pool is correctly specified, the performance will be very close to a traditional hardware RAID (and significantly better than something like the B120i). Furthermore, in certain specific use cases (such as when your working-set fits on ARC)... then ZFS will kill just about everything else in the room - dead.

 

...and that is before you consider the benefits of native COW etc.

 

Of course the P series Smart Array's are generally very good, but I eventually lose my enthusiasm with folks that put relatively minimal amounts of fan noise above powerful storage features.

 

Actually, I owe HellDiverUK a proper apology for being an clown about this last week in another thread.

 

For what its worth - I apologise and admit my retort was not in the spirit of this happy little forum.

 

It is nearly christmas, happy holidays - I'd like to hang around if you'll all let me  B) ...if not I can stay angry at my command line in my lab.

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