[HCoop-Discuss] Finalizing Hardware Upgrade

[Clinton Ebadi]

Peter Gammie <peteg42 at gmail.com> writes:

> On 10/11/2009, at 11:49 AM, Clinton Ebadi wrote:
>
>> The Hardware RAID in the PowerEdge series has a 256M battery backed
>> cache making it pretty fast and resilient against power failure
>> (according to the docs it can lose power for several *days* before
>> losing the write cache; since we'd be using it for our most heavily  
>> used
>> file system its performance is pretty essential.
>
> This seems to be a non sequitur to me: I'm concerned about days of  
> outage as the entire RAID gets rebuilt, if the controller carks it and  
> no compatible card is available.

Even with the basic Dell warranty (that comes with all hardware) a part
would be at the datacenter within 24 hours after failure. 24 hours
sucks, but we could get this down to 4 (and with a Dell tech doing the
onsite visit and install) by going with the best Dell warranty (it costs
a few hundred dollars).

> In utter ignorance, I wonder if the performance of software RAID is so  
> much worse than hardware RAID. I grant that Linux has had some nasty  
> interactions amongst the various parts of the filesystem in the past  
> (e.g. NFS and ext3 IIRC) that might make hardware RAID more reliable  
> anyway.

I think soft RAID1 is about as fast as hardware RAID, but RAID5 involves
some XORing and checksumming that benefit from hardware assistance. How
much this matters in practice I am unsure.

> I know some people who do run large (multi-terabyte) RAID setups, I  
> can enquire what they do if you like.

That would be helpful; I am basing the decision to go with hardware RAID
merely on us using it now in deleuze.

-- 
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