[CentOS] Netcell RAID cards -- 2.6.12.3+ (or 13.2+?) ATA has NetCell support

[Bryan J. Smith]

Ugo Bellavance <ugob at camo-route.com> wrote:
> Anyone tried netcell products

NetCell's RAID-XL is basically a fixed 32-bit (2+1 drive) and
64-bit (4+1 drive) [S]ATA RAID-3 implementation.  Before I
talk more about how RAID-XL works, let's talk RAID-3.

RAID-3 and RAID-4 use striped data with dedicated parity,
whereas RAID-5 uses striped data and parity.  RAID-4 and 5
stripe large blocks, so multiple access could be possible
(reducing latency), whereas RAID-3 writes sectors immediate
and [virtually] parallel to all disks.

RAID-4 and RAID-5 are used in servers where lots of random
I/O is occurring.  RAID-4 is most ideal for large reads and
writes, where latency on the parity disk is not a concern
(e.g., NetApp often uses RAID-4 because NFS v3 blocks are
typically 32KB).  RAID-5 is most ideal for lots of smaller,
random RAID reads and writes, because the parity is also
striped.

RAID-3 is most ideal for desktops with limited processes
writing to/from the disk.  RAID-3 attempts to push as much
data parallel to the disks directly.  The NetCell approach
does this by using 2 ATA disks (16-bit wide data each), plus
1 parity, for it's 32-bit cards, and 4 data disks (again,
16-bit wide data each), plus 1 parity, for it's 64-bit cards.
 XOR (parity) is calculated in-line by the on-board
microcontroller in real-time, and written to the parity disk,
and has up to 128MB of DRAM for buffering as necessary.

I would _not_ use the card for a traditional server.  But for
a desktop, workstation or media server where you want burst
disk access for only a few processes, it's RAID-XL is most
ideal -- especially the 5-disc, 64-bit card.  I have the
SR5000 myself.

> on Centos 3 or 4?

Only updated Fedora Core 3/4 kernels (read on).

> They claim driverless operation under WinXP,

Well, Windows XP has some serious "identity crisis" issues
when it comes to ATA -- especially through different service
packs and hotfixes.  I've documented those in my various
notes on XP, postings, etc...

In a nutshell, for NetCell, you need a hotfixes after SP2,
and there are some recommended for pre-SP2 as well.

> but in linux
> the only doc that is related with CentOS would be the
Fedora
> core 2
(http://www.netcell.com/support/Fedora_Core2_readme.txt)
> and requires a kernel rebuild.

In Linux, the PCI ID and ATA DMA support is added to the ATA
driver.  This is why it requires a kernel rebuild.  As of
kernel 2.6.12.3 (IIRC -- could be 2.6.13.2?), the NetCell
products are now supported in the stock ATA driver.

Since the NetCell is designed for desktops and direct I/O, it
doesn't make sense to use a traditonal SCSI driver.  There
are no real services, queuing, etc...  It's really best as a
"dumb block ATA device" that is written to and read from
directly.  That's why it was designed to show itself as a 1
or 2 device ATA channel.

> I'd like to know if it would be possible to install 
> CentOS directly on drives on such a card, without needing a
> build box...

You'd have to rebuild the installer with a newer kernel like
2.6.12.3.  I had tried to patch the ATA support in before,
and it was a bit of a PITA.  But I am running my SR5000 card
in a Fedora Core 4 test system, using five (5) Seagate 7200.8
200GB drives.  Thing moves data like I've _never_ seen.

I'm using my SR5000 for a prototype multimedia server in my
house.

> http://www.tomshardware.com/2003/11/28/kill_scsi_ii/

Yes, and Tom's showing off single process benchmarks -- like
most enthusiast sites.  Look at them as viable for
desktop-only evaluation.

Start throwing a few other processes at it and you'll quickly
appreciate why 3Ware, Areca, LSI and other cards are better
for servers.  ;->



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