[mythtv-users] 64bit IDE RAID options?

Trey Boudreau trey at treysoft.com
Tue Jan 10 02:53:58 UTC 2006


On Mon, Jan 09, 2006 at 07:42:28PM -0500, Steve Adeff wrote:
> On Monday 09 January 2006 17:36, Trey Boudreau wrote:
> > On Mon, Jan 09, 2006 at 12:26:18PM -0800, Yeechang Lee wrote:
> > > James C. Dastrup <jc at dastrup.com> says:
> > > > Is anyone aware of a PCI-X  64bit / 133MHz capable IDE RAID HBA?
> > > > Or, how about a PCI  64bit / 33 Mhz MHz capable IDE RAID HBA?
> > >
> > > People generally consider 3Ware's 7xxx (ATA) and 8xxx/9xxx-series
> > > (SATA) cards, which all support 64-bit/66MHz PCI-X, the standard for
> > > high-quality, reasonably-priced, true hardware RAID cards. (Or just
> > > for JBOD, as I'm doing with two 7506-4 cards and eight 400GB ATA
> > > drives I'm using in part for MythTV.)
> >
> > I *really* like the performance of my Areca ARC-1120 8 port SATA PCI-X
> > card.  It beats the pants off of my 3ware 7450 and 8506.  I don't know
> > how it compares to  the 9xxx-series controllers.  Unfortunately, the
> > last time I checked the Areca folks hadn't got their drivers into the
> > kernel tree (2.6.14-mumble).  It annoyed me to have to unpack the
> > archive and tweak the Kconfig file, but I eventually got over it
> > (mostly ;-).
> >
> > -- Trey
> 
> whoa, $600 for a controller card!  I think I can live with software RAID, 
> rather spend the money on a faster cpu...
> 
No amount of CPU cycles will get you the disk bandwidth lost to software
RAID5 back:

Hardware RAID5 write of one 512-byte disk block:
write 512 bytes over PCI
(controller card updates the parity without causing PCI bus activity)

Software RAID5 write of one 512-byte disk block:
read 512 bytes of parity over PCI
write 512 bytes of data over PCI
write 512 bytes of modified parity over PCI

At best you can amortize the parity I/O over "n" blocks, where "n"
equals the number of disks in your RAID5 set minus one.  Given MythTV's
propensity for creating large files, you can get this level of
performance much of the time.  Even so, you never get those bus cycles
back.

-- Trey


More information about the mythtv-users mailing list