Raid Card controller for FC System

[Roger Heflin]

Todd Denniston wrote:
> Roger Heflin wrote, On 03/24/2008 02:20 PM:
>> edwardspl at ita.org.mo wrote:
>>> Alan Cox wrote:
>>>
>>>> On Sun, 23 Mar 2008 15:39:22 +0800
>>>> edwardspl at ita.org.mo wrote:
>>>>
>>>>  
>>>>
>>>>> Dear All,
>>>>>
>>>>> Which model / type of ATA Raid card controller is good for work 
>>>>> with New FC System ?
>>>>> Would you  please recommend ?
>>>>>   
>>>> Almost every 'raid' controller for ATA devices is just driver level 
>>>> raid,
>>>> so equivalent to using the built in lvm/md raid support that works with
>>>> any devices. At the high end there are a few hardware raid cards but 
>>>> they
>>>> rarely outperform ordinary ATA on PCI Express.
>>>>
>>>>
>>
>> Edward,
>>
>> The cheapest 4-port raid cards are typically $300US, the 8-port cards 
>> are quite a bit more.   If you are a home user I would suggest not 
>> wasting your money on the HW raid, and has others mentioned it is not 
>> really worth the extra money for a home user, so use software raid.
>>
>> Most of the cheaper cards are fakeraid and at best (if supported under 
>> DMRAID) are only slightly better than software raid.
>>
>>                              Roger
>>
> 
> So would the better question be:
> Which model / type of ATA multi-port card controller is good when you 
> want to do software RAID with New Fedora System?
> i.e. which manufactures cards that you can hang 4+ drives off of, have 
> enough independence[1] between drives, that doing software RAID works 
> fast[2]?
> Can you get 4+ port SATA cards that don't claim to be "RAID" cards?

Yes.  The problem is if you have a PCI (not -E or -X) the bus is limited to 
about 130 MB/second for all cards, so for a fast machine you need either -E or 
-X and multi-port cards of those get expensive too.

I have a crappy (but cheap) 4-port SATA SIL card, it works, it is PCI and not 
the fastest but it is cheap, and appears to be reliable, it only does about 
60MB/second writes and 90MB/second reads with 4 disks under RAID5.

If you need speed and more than 4 ports, the cost goes up quite a bit.

And you have to test them, I have seen cards that each 2 sata ports share 
hardware, so using 2 disks on ports 1 and 3 is faster than using 2 disks on 
ports 1 and 2, and of course all of the ports share the bus the card is plugged 
into, so it is critical to test things as none of the specifications will 
actually tell you any of this.

A lot of the highpoint fakeraid cards are based on the Marvell sata chipset(s) 
and perform pretty good, but you have to actually confirm that the given version 
is truly supported under Linux without their extra driver, and they are 
reasonably cheap.   I have not tested the recent multiport Adaptec controllers 
so I don't know what they will do.

On motherboards you have a similar set of issues, depending on where the given 
motherboard connects in the Sata controllers depends on how much the total 
throughput could be.   Some put the sata controllers on the PCI (non-X non-E) 
bus part which makes them truly suck, and some put things closer to the cpu and 
on higher bandwidth parts of the mb/chipset, you need to look at the MB's block 
diagram to figure out exactly what is shared with what to determine the best 
config to get the most speed out of things, and what other components on the MB 
can affect you (network..)

> 
> Or has everything already been said here:
> http://linuxmafia.com/faq/Hardware/sata.html
> http://linux-ata.org/faq-sata-raid.html
> 
> [1] I am making the old assumption that ATA drives on the same bus slow 
> each other down.  Does that really matter with SATA?

Depends on the SATA card's chipset, generally with the newer ones it does not 
matter.

> 
> [2] assuming the controller card is more likely to be the bottleneck 
> than the processor, PCI bus, or drives.
> 

Unless you have a huge number of disks, and good bandwidth everywhere, the 
answer is one of the busses to the SATA card will probably be the bottleneck, I 
have had 3+ year old quad socket MB's with PCI-X sustain 360MB/second read or 
writes with the bottleneck in that case being the 2-2Gbps (about 440MB/second 
limit) fiber channel ports being used, in that case though I had several 
external raid units attached to the machines each of which was quite fast, and 
had I used more ports on separate PCI-X buses could have probably easily 
exceeded that rate, but the spec we were trying to meet was met by the 
360MB/second so there was no need to go to more extreme measures.

It comes down to, you need to know how a given MB allocates its bandwidth, and 
what the limits are where things join together to even be able to guess before 
testing what is going to be the limit, and you need to know what you actually 
need for a given application.

                                   Roger