[CentOS] Serial ATA hardware raid.

Fri Apr 15 20:15:35 UTC 2005
Bryan J. Smith <b.j.smith at ieee.org>

From:  Franki 
> The 3ware 9500 goes for $1023 AUD.
> once I add some fast drives to that this thing is starting to look like an expensive upgrade.

RAID-5 is only ideal for lots of contiguous reads or disk storage efficiency.
If you have more writes, or more random reads, then RAID-0+1 is better.
Then the 8506 does nice for less.

> My main wholesaler sells Adaptec stuff,

I live 5 miles from one of Adaptec's major support centers in the 1,006 acre University of Central Florida Research Park.
I know many Adaptec employees.
Adaptec still does not officially support Linux for RAID cards, only standard SCSI adapters.
And unlike LSI/Symbios, who treats OEM and retail the same (making suppor easier),
Adaptec is retail focused, and produces variants for OEMs that are quite compatibility nightmares.

> http://www.techbuy.com.au/products/34526/I_OCARDS_HARDDRIVECONTROLLERS/Addaptec/AAR2410SA/AAR2410SA_4-Port_Serial_ATA_RAID_Card_-_RAID_0_1_5_10_JBBOD.asp
> For $450 it is a 4 port controller and has onboard 64MB ECC cache.

Adaptec's aging 2400A/2800A series are 66-100MHz  i960/IOP30x series based on their former DPT acquisition.
In fact, before their DPT acquisition, they had virtually *no* i960 or StrongARM solution that worked with Linux.
Since then, the support has been varied, although the dpt_i2o driver seems to work with most products.
Intel designed I20 for its i960 to make drivers and user-space software more uniform compatible,
but only a few vendors (like DPT and LSI) took advantage of it.
I used to have DPT and LSI i960 SCSI RAID controllers on Linux, NT, OpenVMS and UNIX on a variety of non-PC platforms like Alpha and MIPS.

But, as I mentioned before, the i960/IOP30x is a *massive*slouche* for today's drives.
The ones used in the 2400A/2800A series were fine 5 years ago, but don't even bother with the 28x0 and the 24x0's i960 is going to be the  bottleneck.
And then you have the fact that Adaptec is "hands-off," officially, on the dpt_i2o driver.

Get a 3Ware Escalade 8506-4 for about the same price, and either run RAID-5 if you have lots of reads, or RAID-0+1 if you are doing lots of writes (especially random).
Yeah, you'll lose a disk in the effective storage for RAID-0+1, but I've yet to see an application where RAID-5 could beat RAID-0+1 on any  controller.

> But Alexander on the list here said that adaptec is questionable
> for Raid cards. The last time I had an Adaptec anything was a 2940UW Scsi controller
> and that thing gave me years of good service.

Retail, of course.
For those of us with OEM versions, Linux compatibility is a nightmare.
Why can't Adaptec be like LSI and just have one set of firmware?

> Not sure what to chase up now. :-(
> Does anyone have any experiance with the above adaptec card?

At RAID-5, it only beats the Escalade 8506 at random writes where the measly 2-4MB SRAM oveflows.
But then the Escalade 9500S with 128MB+ of DRAM buffer (in addition to the ASIC+SRAM cache)  wipes the floor with it because it doesn't have a 10 year-old i960 behind it.

When it comes to non-writes (or RAID-0, 1 or 0+1 non-blocking), its 32-bit blocking/buffering i960 microcontroller+DRAM bottleneck looses badly to the 64-bit non-blocking/caching ASIC+SRAM design of any 3Ware product.
And 3Ware writes the GPL drivers in the kernel, which have been included since 2.2.15 (yes, 2.*2*.15).

3Ware's 3DM2 suite is also very nice for user-space monitoring.
And yes, you can load 3DM2 from the 9500S download on the older 7000/8000 series (just not the 6000 series).

BTW, performance matters *little* if you are putting your storage controller on the same bus as your NIC.
Especially if it's a measly, "shared" 33MHz PCI32 bus.
You might as well use 2 hard drives in RAID-1 because you're going to saturate it - let alone your GbE is going to be "fighting" it.

Get a mainbaord with PCI-X, or at least get a chipset with the GbE on a HyperTransport interconnect or PCIe x1 rail so it's not fighting the  storage controller for the PCI bus.
Of course most chipset GbE and 99% of GbE cards are poorly designed  (8-32KB of SRAM is typical, 64KB is you are lucky),
and one should get a GbE card for a server with at least 256KB SRAM.