vSwap + Burst at the same time?
Hey guys, I'm usually the quiet one, but have a discussion with a provider right now in terms of this:
Can you have the following specs for a VPS, at all?:
128MB guaranteed RAM
256MB Burst on top
128MB vSwap just in case
So basically, vSwap and Burst at the same time - possible or not?
I'm only a VPS user, not somebody who works behind the scenes with OpenVZ, hence I ask you guys :-)
And it if is possible, how would it "look like"?
I give you my take, not sure how right or not right it is:
It could be that you can't have both, considering they are "old" and "new" techniques OpenVZ uses afaik. BUT, as I don't know, IF it were possible, it would, from within a VPS look like this:
free -m would show something like this:
total used free shared buffers cached
Mem: 384 50 334 0 0 32
-/+ buffers/cache: 18 366
Swap: 128 0 128
and beancounters would be setup to reflect the assignment of 128MB to guaranteed and the 256MB to Burst. At least that's how a system with Burst and "normal Swap" would look like.
So what do you say guys?
Thanks in advance!!
Samuel
Comments
that is possible from what i know. this is what i got from hostigation december deal
vswap is the new burst. Actually it is different from burst but it is all you get with centos 6.x and up.
Nice, two contradicting answers :-) Any VPS-host who wants to jump in? Please?!
Why would you want a VPS host to jump in? Most of them don't know anything. You'd be better off asking at http://forum.openvz.org/ and waiting for someone who actually develops OpenVZ to respond.
Anyway I'm not sure if it's possible, but SolusVM says it does not allow it when you configure VM through it. Following is just conjecture: Even if it were possible in OpenVZ, the system would probably be unstable. Anyway vSwap is meant as a replacement to burst, since it manages the memory better and the speed of vSwap would still be the same as other memory (edit: there is artificial slowing to emulate normal swap). So 384 MB vSwap would be better.
Edit: it seems like it is possible, just don't see why you would want to use it. Since you can have vSwap assigned and then set oomguarpages.
@perennate
The speed of VSwap would not be the same, the system slows it down to emulate swapping. Also if the memory on the hostnode is full it uses the nodes swap space instead of memory for the vswap
So? Swap space may be used for other memory too.
@perennate
So.. you stated the speed of vswap would be the same, in theory it would not as it is artificially slowed down to emulate the speed of actual swap
Yeah, that's true.
Yes you can do like 256mb ram then burst upto 512mb
then add 128mb swap so once 512mb is used any after that its using vswap which slows down container.
So the extra 256 burst is an actual burst the 128mb vswap is your container slowed to mimic swapping.
This is from as far as i am aware.
@VPSSimon
Not sure about that, I believe in SolusVM it is only currently possible to have either VSwap OR burst. May be wrong on that.
According to http://openvz.org/VSwap you can still have UBC parameters with vSwap, so it should be possible to have both burst+vSwap.
@perennate Fair enough. Don't believe SolusVM supports it however, if the hostnode is CentOS6 I believe solusvm pretty much ignores the burst value field.
Partly right, On plan creating it shows only ram an burst which is vswap
Edit resources for each VPS manually an you get more options oddly.
Upgrade/Downgrade via Custom Settings
Guaranteed RAM MB
Burstable to RAM MB
VSwap MB
@VPSSimon I noticed that too but I believe I tested it before and it ignored the burst value on CentOS 6, may be wrong?
So SolusVM doesnt support when making plans but you can manually edit a VPS resource plans to do it
Dont ask me why its like that; I have no clue.
An i haven't gone into testing it to much to confirm or deny. sorry.
http://docs.solusvm.com/openvz_vswap says it's not possible through default config, but I guess custom setting maybe.
Edit: anyway I still don't see the point, sure it's slower but how much so? And is that not worth the better memory management?
you could be correct. Haven't tested to confirm.
Plan creation calculates vSwap based on Burst Memory - Guaranteed memory, individual manual configuration of the settings per VPS does not use the same setup for that, using the vSwap field as expected.
Well you cleared up the confusion with precise answer
makes sense they do calc for plan part an custom lets u really customize it. Although surely if its there its taken into account. rather than ignored.
Our plans have vSwap setup based on the Burst - Guaranteed metric, but here's what a provisioned VPS looks like in the Solus panel if you go to edit it:
And the Resource Usage section:
When you DISABLE vSwap, you get expected results:
I'm pretty sure this isn't possible as VSwap replaces the UBC system. On a VSwap host the old UBC system does work, but I'm certain you can't combine VSwap + Burstable RAM.
Source: as a provider (Afterburst) & http://wiki.openvz.org/VSwap
Isn't burst just setting privvmpages > vmguarpages or something?
On CentOS 6 (2.6.32 kernel) based OpenVZ you can ONLY have vswap.
On CentOS 5 (2.6.18 kernel)based OpenVZ you can ONLY have burst.
Clear enough?
The confusion probably comes from the way the Solus CP presents it by making the Burst/Vswap the same setting.
This is what I bought from Hostigation, 512mb OVZ burst to 1024mb. It seems a burstable to 1gb but on .32. not sure
uname -rwill show you the kernel rev. your free m tells me u are on 2.6.18 kernel...or vswap just set to 0.Yes - it uses two old UBC values (ram+swap), all the others (including burstable ram) will be ignored.
Wow, that's a lot of messages after the weekend lol So basically like I expected, there is no such thing as guaranteed RAM + Burst + vSwap at the same time and we (buyers) now have to settle for slower vSwap instead of Burst, is that it? Not exactly good news for people paying for the VPS, good news for providers though. (I want my burst back!
)
Burstable RAM is problematic. Some applications expect the presence of swap, and if there is none they go crazy. Also, some clients decide to use their burstable RAM 100% of the time (which is sort of not what it's intended for. BURSTABLE RAM!) which can throw off node usage statistics. vSwap, since it's slower, is less likely to be used 100% of the time, though it's still in the node's RAM, so it's not super slow. Java also goes insane in the presence of Burstable RAM. As in using ever increasing amounts of RAM. vSwap is actually a nice thing, one which I'll be happy to see rolled out for BlueVM's customers once Feathur is put into place and we can FINALLY move away from the 2.6.18 kernel line. HyperVM, you've been nice but it's time for you to GO AWAY!
I would suggest you adjust your thinking. Sounds like you are getting hung up on the marketecture rather than the actual reality of it. You seem to think that with burst you were getting something for nothing and providers were just giving it away or whatever. If you need more memory get a plan with more memory. It all comes out the same. There is only so much memory on the server either way. Maybe your current provider just hasn't adjusted their plans/pricing yet or you need to find a new provider.
We never used or advertised burst because it was always kind of a bogus feature as far as we were concerned. A plan with 400MB burst and 200MB RAM was the same as a plan with 400MB RAM. So just sell a plan with 400MB RAM. Only time it starts to make a difference is when the server is out of memory + swap which should never be allowed to happen. The server would be so loaded down it would be almost useless. If you were running your VPS well into your burst and that happened your VPS would be basically crashing constantly because the server would be shutting down all your necessary processes running in burst. So add it up and it's a bogus feature that is only useful in a situation that should never be allowed to happen in the first place.
sman, with all due respect, insulting me doesn't help. On top, that statement you made is just wrong - I suggest you first read about what Burst is and what vSwap is and then, maybe, try again and don't confuse reality with "your way of thinking". Just saying, you'll fall from your "high horse" if you try to belittle others, not nice.