On 07/10/2017 10:09 PM, Per Jessen wrote:
Rüdiger Meier wrote:
I have never benchmarked any advantage for hardware raid. Actually I found Linux softraid always faster. I guess that it's the reliability which matters.
Yes, reliability and serviceability are key. I guess I could do some actual benchmarking at some point, but performance is secondary.
HW Raid is usually - OS independent, even inclusive remote storage administration, monitoring etc. - certified for (only) certain hard drive models. So that one can be sure that the whole chain (battery backup-ed Cache, HD cache, etc. will survive a power failure without inconsistent file systems.
We have been using 3ware/LSI and HP Smart Array Controllers for more than 10 years, none of them have required certified drives sofar.
I have had many incompatibilities between Adaptec Controllers and certain drives but never any problem with onboard controllers. Anyways with non-certified drives you can't be sure that everything works as the controller expects. There are drives where you can't disable write cache or which are just "always fast", telling the controller that everything was written although it's still cached. Other drives don't validate checksums or whatever. I've read an interesting article about these issues a few years ago. There was a client/server based test script producing heavy load. It was able to validate the written data after one pulled the plug and rebooted. Surprising results. My conclusion was that it makes no sense to waste money for expensive controllers without testing the whole system and drives. Now I'm using only SW Raid with onboard controllers or cheap HBAs, IMO faster and more flexible. cu, Rudi One annoying
issue is their insistence on a battery for the write cache. Our older HSG80 fibre controllers had an option "site-wide UPS". Newer HP conrollers do have that option too.
If you want reliability you need to have a controller cache with battery/capacitor
Unless you have site-wide UPS.
and turned off HD write cache. If you don't have a battery you have to turn off any HD write cache.
Right.
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