[CentOS] Serial ATA hardware raid.

Fri Apr 15 19:45:21 UTC 2005
Bryan J. Smith <b.j.smith at ieee.org>

From:  Harald Finnås
> 3ware (7500, 8500, 9500) is IMHO best bet on all distros

3Ware includes a GPL driver in the stock kernel.
Although as with any "intelligent" storage adapter, you should verify the driver, firmware and user-space tools are compatible.
I need to get my FAQ out showing 3Ware releases v. Red Hat updates.

The 3Ware 7506/8506 are of the same 64-bit ASIC 66MHz PCI64 storage switch.
They are non-blocking (like a network switch) thanx to their ASIC+SRAM (static RAM) design and kill at RAID-0, 1 and 0+1.
While they are also high performing at RAID-5 reads, the small amount of 2MB (-4, -8) or 4MB (-12) SRAM can overflow on random, RAID-5 writes.
The 3Ware 9500S series adds 128MB+ SDRAM to help buffer these overflows.
Unlike RAID-0, 1 and 0+1, RAID-3/4/5 are always blocking/buffered I/O, so the ASIC+SRAM design goes from an advantage to a liability.

So if your application calls for lots of random writes, either use RAID-0+1 or get a 9500S for $50-200 more.

> I also run it on an LSI SATA controller,
> but I cannot remember the  exact model.
> But I can find it if you want to know. :)

Unless the model says "X" (for XScale), you don't want it.
Pre-XScale (StrongARM lineage) microcontroller+DRAM designs are *dog*slow*.
Intel i960 (including IOP30x series) can't push much beyond 60-70MBps.
While that was sufficient for yester-year's drives in RAID-3/4/5, it is not today.
And blocking/buffered is never ideal for ATA.

The StrongARM and, subsequent, superscalar XScale microcontrollers change everything.
They can push as little as 200MBps in old designs up to 500MBps in the new IOP32x/33x series.
But you'll pay through the nose for the cards, $500+, although they do best even the 3Ware 9500S at RAID-5.
Some have RAID-3/4 options that are more ideal than RAID-5 for desktops and NFS servers, respectively.

But if you are looking for maximum performance, reliability and compatibility as well as load-balanced reads, RAID-0+1 on a sub-$300 3Ware Escalade 8506-4 (or a -8 for a little more) is pretty much unbeatable.
The 9500S is overkill for just RAID-0+1, and if you're doing lots of writes, it's typically going to be faster than any RAID-5 solution.

For extreme performance with disk redundancy, consider (2) 3Ware 8506 cards in an Opteron system with an AMD8131 or AMD8132 dual-PCI-X bus  HyperTransport Tunnel -- with each card on their own PCI-X bus and then their individual RAID-0+1 volumes in a single LVM2 stripe set (RAID-0).
Connected to a GbE in the HyperTransport interconnect or, better yet, a HTX (HyperTransport) 10GbE (just coming out) or InfiniBand (upto 1.8GBps actual performance on HTX) and you're slapping silly anything Intel can offer with either Xeon or Itanium over PCI-X by a factor of 2-3x.