Data loss could conceivably occur on shutdown or restart too - just saying... You are assuming that the data that doesn't get written to disk is going to be non-essential... I wish you good luck with that. I think if one doesn't want to be an idiot, one would not enable a cache that has no means to ensure that the cache is written to disk.
I think your take away from all of this is somewhat misdirected. Not having a BBU simply means that your writes really should always be synchronous/immediate. That shouldn't really be a problem and shouldn't impose a large performance penalty.
Your performance issue relates more to the fact that RAID 5 implementation on the 3Ware cards is rather poor and modes such as RAID 10 (RAID 0 + 1) will give you much more speed that you realize. If you also consider on the surprisingly higher rates of failure with loss of data possibility when reconstructing a missing/dead drive on a RAID 5 setup you really should be re-examining your storage strategy.
Craig
On Sep 1, 2011, at 5:43 PM, Austin Godber wrote:
> At this point the card is pretty much useless without that cache enabled. Without recommendations for making writes of 256MB or larger files faster without this cache enabled, I will have to accept the possible data loss in the event of power outage. If it is only the case of data loss during a power outage, I will take that ... rather than failure to write at all during 99% of my usage.
>
> I will, for the sake of not being an idiot, look into buying the BBUs.
>
> Austin
>
> On Thu, Sep 1, 2011 at 4:49 PM, Tom Bishop <bishoptf@xxxxxxxxx> wrote:
> Keep in mind you really only want to enable the cache if you have a
> bbc, otherwise you are risking your data since it can/will cache
> writes...just something to keep in mind.
>
> On 9/1/11, Austin Godber <godber@xxxxxxxxx> wrote:
> > Hi Craig,
> >
> > Thanks for the suggestion. I would if I could. I'd also probably try
> > another file system. Though the good news is, enabling the write cache on
> > that array has improved things significantly. Which, in my case, was:
> >
> > tw_cli /c2/u0 set cache=on
> >
> > Now, if only I had the battery backup unit for the card.
> >
> > Thanks, everyone for their suggestions. For now I am happy with the
> > situation, but I'd be interested to hear the experiences of others.
> >
> > Austin
> >
> > On Thu, Sep 1, 2011 at 3:58 PM, Craig White <craig.white@xxxxxxxxxx> wrote:
> >
> >>
> >> On Sep 1, 2011, at 1:41 PM, Austin Godber wrote:
> >>
> >> > Hello,
> >> >
> >> > Does anyone have experience using a 3ware 9650SE series raid controller
> >> on CentOS 6.0?
> >> ----
> >> use RAID 10
> >>
> >> Unless something has changed, RAID 5 is notoriously slow on the 3Ware
> >> controllers. Whatever you do will only incrementally speed things up. If
> >> performance is desired, RAID 5 is not the way to go.
> >>
> >> Craig
> >> _______________________________________________
> >> CentOS mailing list
> >> CentOS@xxxxxxxxxx
> >> http://lists.centos.org/mailman/listinfo/centos
> >>
> >
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