separate SWAP and DUMP devices v/s having SWAP+DUMP configured on the same device?

[Mike_305]

Hi,

I have few questions on SWAP and DUMP.

1) Is there an advantage or disadvantage in having separate SWAP and DUMP devices v/s having SWAP+DUMP configured on the same device?

2) How much swap and dump do I need with 4 GB memory on L2000 system running
Oracle financials?

3) Is there a document with this information?

Thanks in advance.

Thanks,

Mike

[Pete Randall]

Mike,

A frequent question - one that you might want to try searching on something like +"swap" +"dump". Use the search button to the far left, click on boolean, click on search the forums, click on search - voila.

Pete

[Pete Randall]

Curtis Larson has a lot of good info in this thread:
http://forums.itrc.hp.com/cm/QuestionAnswer/1,,0x00c06af52b04d5118fef0090279cd0f9,00.html

Pete

[S.K. Chan]

This is the document you're looking for ..
(DocID= KBRC00008468).
http://support2.itrc.hp.com/service/cki/docDisplay.do?docLocale=en_US&docId=200000058465590
That should answer question 2 & 3. For q1, in my opinion it does not matter because it's bound by how much swap you got configured and is that swap size enough to save all you dump information ? From the document you should be able to determine how much dump sapce you need, once you got that number, compare it with your swap space (primary swap which has dump in it too), if it's enough, then fine. If it's not you may need to configure multiple dump area which can reside on a different logical volume other than that of swap.

[Sean OB_1]

Check this thread out: http://forums.itrc.hp.com/cm/QuestionAnswer/1,,0x00c06af52b04d5118fef0090279cd0f9,00.html

[S.K. Chan]

Just in case .. if you ever need to configure additional dump space (it's best to put it in vg00 if you got 10.20 this is a MUST), this is how you do it ..
Eg, creating 500MB of additional dump space in vg00 (lvol8)..
# lvcreate -L 500 -n lvol8 -C y -r n /dev/vg00
==> Bad block relocation off and MUST be contigous.
# lvlnboot -d /dev/vg00/lvol8
==> Turn it on !

[harry d brown jr]

1) I NEVER separate the two. The likely hood of me sending in a dump to HP is about as likely as clinton explaining what "is" is!

2) Depending upon the amount of memory, I usually do 1.5 times memory for swap, BUT because we can a lot of memory in a server, that's not always practical. If I had a machine with 12GB of memory, there is no way in hell I would create an 18GB swap area. For 4GB, I'd set up a 6GB swap/dump area.

3) Oracle has their documentation, and a lot of us have our own ideas. My question is this: Is 4GB all you plan on for Ora-Fin? I think I'd toss at least 6GB at it, with 4 CPU's in that L'.

live free or die
harry

[Mike_305]

Hi,

What if I activate "psuedo swap option"?

Thanks,

Mike

[keith persons · Accepted solution]

Psuedo-swap may help or hurt depending on overall memory utilization. If you don't anticipate memory being highly utilized, psuedo-swap will probably help. If memory will be heavily utilized, you're probably better off creating additional swap device(s).

The main benefit of psuedo-swap is a reduced need for physical swap devices/files during initial setup and operation. The 'old' rule of Unix was 2-3 times memory for physical swap and adjust according to actual needs; this has become impractical due to physical memory capacities.

If you can enable psuedo-swap, your physical swap can be smaller than your actual memory but again, it depends on overall memory util.

Dump space has become a different point of perplexity for sys admins - full dump space needs to be size of phys memory + 4 pages. The question becomes whether you intend to send in crash files for analysis and, will a partial dump be enough or will a full memory dump be needed?

More commonly, the current (non-mission critical) approach seems to be forgo the full dump space to start. Should it prove necessary to configure for a full dump it can be addressed at that time.

[Mike_305]

Hi Keith,

Since, you answer about psuedo-swap. My memory usage is about 80% on my system. Can you please tell me what will happen in that case.

Thanks,

Mike

[keith persons]

Mike,

ooo, 80% util, I'm less prone to suggest psuedo-swap with util this high. My reasoning factors in the probability of growth, few systems are truely static. Should memory util increase with psuedo-swap enabled, the result could be a thrashing condition. Better to be a little conservative and prevent this than take a chance of disrupting production.

Generally, under your circumstances, I'm more prone to advise adding swap devices to avoid prompting unwanted memory pressure.

Hope this calrifies things more.

[Jeff Schussele]

Hi Mike,

I'll play Devil's Advocate here & give you an argument & situation where having seperate swap & dump would be desirable:

That would be on a production system that in the normal course of operations is always into swap.
If the system dumps, you'd have to wait for the contents of swap to be written out before the dump could be completed. Depending on the size of swap & it's utilization at crash time, this could be a significant amount of time. And in production downtime is a sin. The need to get the prod box back on-line ASAP would dictate that you have sep swap & dump as in this case the dump could be written in the background while the system boots.

Now I can here all of you & yes there should be more memory in that system. But we all know that as much as we'd like to control our own boxes, there are times when you just don't get what you need let alone want.

My 2 cents,
Jeff (been there seen that)

[Mike_305]

Thanks