Re: Software RAID and TRIM

[Werner Fischer <devlists@wefi.net>]

On Mon, 2011-07-18 at 11:53 +0100, Tom De Mulder wrote:
> On Sun, 17 Jul 2011, Lutz Vieweg wrote:
> 
> > What is really an important factor for SSD performance: The controller.
> > The same SSDs perform with significantly lower latency for us when
> > connected to SATA controller channels than when connected to SAS
> > controllers (and they perform abysmal when used as hardware-RAID
> > constituents, in comparison).
> 
> Interesting.
> 
> I think it depends a lot on the controller. On a Dell server with PERC5/i 
> RAID controller (actually made by LSI) I saw some performance degradation 
> but not enough that I'd consider it a deal-breaker for situations where I 
> really cared about the RAID functionality, more than about the loss of 
> performance. After all, the latency is still massively lower than it is 
> with spinning disk.
> 
> I have a really great Areca RAID controller in a different server, but 
> unfortunately it's in use and it'll be a while before I get another one I 
> can use for testing. Given how well it does in other respects, I have high 
> hopes for it.

I agree that the controller can influence performance:
1. SATA controller: direct communication
2. SAS controller: Serial ATA Tunneling Protocol (STP) is used,
   this can have an impact on performance
3. Hardware RAID controller: depending on the controller, performance 
   impact can be from low to very high

Regards,
Werner

> 
> 
> Best,
> 
> --
> Tom De Mulder <tdm27@cam.ac.uk> - Cambridge University Computing Service
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: Werner Fischer
: Technology Specialist
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