Subject: Re: [vserver] Sponsoring VServer getting up to date with mainline
From: Ed W <lists@wildgooses.com>
Date: Fri, 22 Aug 2008 23:52:30 +0100

Michael S. Zick wrote:
>
> The true advantage of a hardware card, is you only read/write
> the storage data once over the PCIe link.
>   


I agree in theory, but I have been desperately disappointed with a two 
3Ware cards of various generations.  They struggled to get read or write 
performance to match a half that of a single drive in a 4 drive raid5 
config.  Some of the limitations looked very much like those of the PCI 
bus and indeed 3wares benchmarks suggested that you needed faster than 
PCI to get >20-40MB/sec out of their cards (ugg).  To me this looked 
very much like the data was being transferred too many times versus 
theory (also I discovered later that nearly all these hardware cards 
can't do xor fast enough to keep up with a sensible modern disk, hence 
software raid5 can often be faster because you aren't lagging on the xor 
engine...)

I think the safe benchmark is all in software and be very cautious of 
these hardware SATA cards.  That said, the various scsi cards I have 
tried absolutely scream.  Why there are only cr*p sata hardware cards I 
just don't understand?

Oh well

Ed W