[Info-vax] Quorum disk and page/swap/dump files

[RGB]

On Friday, December 6, 2013 9:16:55 AM UTC-5, Stephen Hoffman wrote:
> On 2013-12-06 13:49:29 +0000, RGB said:
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> 
> 
> > We have a 2-node HP rx2800 cluster running VMS 8.4.  As such I have set 
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> > up a quorum disk for the 2-node cluster with the disk having a vote of 
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> > 1.  (Expected votes are set to 3.  Thus quorum is 2.)
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> 
> 
> Given subsequent references to EMC, I'm guessing this is probably on 
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> Fibre Channel, and a Fibre Channel SAN disk would be accessible to both 
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> hosts.  If not and if you're using some sort of local EMC storage, then 
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> the quorum disk won't be useful.
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> 
> 
> > However, that is neither here nor there.  I was only able to obtain a 
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> > 32GB LUN from our EMC folks for use as the quorum disk.  Which seems an 
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> > awful waste of space.
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> 
> 
> Ayup.  Wasting an entire half-of-a-cellphone's worth storage.
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> 
> 
> > Does anyone see any problem with putting the cluster's page, swap and 
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> > dump files on the quorum disk?  I've never done this before and I'm 
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> > hesitant in doing so due to the critical nature, obviously, of the qdsk.
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> 
> 
> Will this work?  Sure.  More than a few folks use a shared boot disk as 
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> the quorum disk.  Some will put a bootable backup root on that disk.
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> 
> 
> This all assumes you're still paging, too.  With the increase in 
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> physical memory, paging is becoming less common.
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> 
> 
> The biggest general concern with the quorum disk is the responsiveness 
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> of the I/O aimed at the disk.  If the quorum disk I/Os get delayed due 
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> to saturation, then the cluster will "burble."  Excessive paging I/O 
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> could cause this, and disk backups have been known to cause 
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> quorum-related cluster connectivity glitches, too.
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> 
> 
> Would I bother with this savings?  I'd ask the EMC folks how tight they 
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> are on storage, and — guessing — they're probably not, and if so then I 
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> probably wouldn't worry about this.  Might stick some licenses or other 
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> common data there for general use, maybe even the cluster common files, 
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> but...
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> 
> 
> (FWIW, there could well be as much interstitial loss on an OpenVMS disk 
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> with large numbers of files and large cluster factors, if not more.  
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> Average loss within an OpenVMS file system is half the number of files 
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> on a disk times the disk cluster factor, and loss can be higher with 
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> some file organizations.  While I'm doing math, 32 GB is ~0.032% of a 
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> terabyte disk, and a one-terabyte disk is a small disk by current 
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> standards.)
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> 
> 
> 
> 
> -- 
> 
> Pure Personal Opinion | HoffmanLabs LLC

Hey Steve,

Thanks for your input.  The EMC folks here are chronically short of storage space, or so they claim, so asking for space is not dissimilar to asking someone if they would like their wisdom teeth yanked out without any novacaine!

The two 2800's in question have 32GB of RAM each.  Therefore that fact, coupled with the type of applications which run on those systems, negates paging to a large degree.  Yes, there is paging activity on the systems but minimal.  No swapping to be seen at all. 

I might leave small-ish page and swap files on the shared system disk and create/install secondary page and swap - albeit larger - onto the quorum disk.
Both of best worlds I guess!

Again, thanks for the input.