drbd-user March 2010 archive
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drbd-user: Re: [DRBD-user] [Scst-devel] ]Re: vSphere MPIO with s

Re: [DRBD-user] [Scst-devel] ]Re: vSphere MPIO with scst/drbd in dual primary mode. WAS: Re: R: Re: virt_dev->usn randomly generated!?

From: Vladislav Bolkhovitin <vst_at_nospam>
Date: Tue Mar 09 2010 - 20:24:12 GMT
To: Zhen Xu <zhenxu_zj@yahoo.com>

Zhen Xu, on 03/07/2010 02:23 AM wrote:
> I wonder how you can do NV_CACHE battery backed. The NV_CACHE in SCST
> is just the system memory/page cache. It is not the cache on the RAID
> card. You could have UPS hooked to the server running SCST. However,
> if the system failed (memory, hardware, or just seg fault) and you had
> to reboot without proper shutdown, the page cache will be lost. It is a
> very interesting setup that you wanted to do. I am interested if you
> have much success.

IMHO, basically, a battery backed RAID card isn't anyhow fundamentally
different from a system with an UPS and possibility to clearly shutdown
on a power shortage. They both have internal power supply, battery,
system hardware, memory and software. The difference is only in the
number of components, hence probability of failure. I think a good
system with good hardware and dual power supply (they often fail on the
first time) should be hardware wise in the same order of magnitude cache
loosing failure probability as the RAID card.

Vlad
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