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From Peter Ondruška <peter.ondru...@gmail.com>
Subject Re: NFS and Derby
Date Thu, 11 Nov 2010 17:18:10 GMT
You could use NFS mounted read only databases as you can do so with
CD/DVD based media.

The risks with read-write databases on NFS devices is (was) that in
the old days of UDP protocol based NFS client/servers your connection
may easily break. It is not the case anymore with decent operating
systems (Solaris for example) and good NFS servers (again mostly
Solaris based or those from famous vendor) and good highly available
network infrastructure. Nowadays your servers disks are likely network
connected anyway (FC SAN, iSCSI).

On Thu, Nov 11, 2010 at 5:18 PM, Donald McLean <dmclean62@gmail.com> wrote:
> A "local" database on an NFS mounted disk? I would never consider such a thing.
>
> My experience with NFS mounted resources is that network congestion
> can cause all sorts of nasty side effects. Even something as simple as
> an unexpectedly slow read or write can cause unanticipated cascading
> failure conditions. And no matter what value is used for a timeout,
> you can pretty much guarantee that it will be exceeded eventually.
>
> I realize that this doesn't address Derby specific concerns such as
> database corruption. Fortunately, I have no experience with that.
>
> Donald
>
> On Thu, Nov 11, 2010 at 10:56 AM, Kathey Marsden
> <kmarsdenderby@sbcglobal.net> wrote:
>> I have always told users they have to have their databases on a local disk
>> to ensure data integrity and that  a system crash for an NFS mounted
>> database could cause fatal corruption, but had a user this morning take me
>> to task on this and ask me to explain exactly why.  I gave my general
>> response about not being able to guarantee a sync to disk over the network,
>> but want to have a more authoritative reference for why  you cannot count on
>> an NFS mounted disk although I did find several places where the sync option
>> "favors data integrity" which certainly doesn't sound like a guarantee.
>>  Does anyone know a good general reference I can use on this topic to
>> support my "you gotta use a local disk" mantra.
>>
>>
>> Also I think our documentation on this topic should be a bit stronger.
>>  Currently we just say it may not work and probably should be clearer that
>> data corruption could occur.  I will file an issue to beef up the language
>> based on the conversation in this thread.
>>
>> http://db.apache.org/derby/docs/10.5/devguide/cdevdvlp40350.html
>



-- 
Peter

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