Vessey, Bruce A
2008-Nov-07 14:01 UTC
[Xen-devel] Questions about certain Xen limits and features
(I previously posted this on the Xen-users list, but received no responses. Hopefully this team can help me.) I''ve been away from the Xen community for a while and, unfortunately, haven''t kept up with its current state. I''m assembling a comparison of virtualization solutions (Xen, VMware, Hyper-V, ...) and I have a few questions about Xen''s current functionality. I''d appreciate it if somebody would be willing to take the time to answer. I''m interested in the current *released* version (i.e. Xen 3.3 -- not unstable) for x86_64. Of course, if you know about on-going work that will change any of these answers, I''d appreciate knowing that too. Thanks, Bruce (1) What''s the largest number of "logical processors" that Xen supports on the host system? For me, this translates to cores. I prefer to keep hyperthreading out of the picture. (I believe that this was 126 in 3.3, but is changing to "unlimited" based on Jan Beulich''s recent work. Is that correct?) (2a) What''s the largest host memory that anybody has tested? (2b) What''s the expected host memory limit (if somebody was able to configure a system that large)? (3a) What''s the largest guest memory that anybody has tested? (3b) What''s the expected guest memory limit (if somebody was able to configure a system that large)? (4a) Does Xen support hot-add of physical hardware to the host system? If so, which devices? (4b) Hot remove? (5a) What''s the maximum # of virtual NICs per guest? (5b) What''s the maximum # of virtual HBAs per guest? (5c) What''s the maximum # of LUNs per guest? (6) What''s the maximum # of powered-on guests per system? _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
Keir Fraser
2008-Nov-07 14:22 UTC
Re: [Xen-devel] Questions about certain Xen limits and features
On 7/11/08 14:01, "Vessey, Bruce A" <Bruce.Vessey@unisys.com> wrote:> (1) What''s the largest number of "logical processors" that Xen supports > on the host system? For me, this translates to cores. I prefer to keep > hyperthreading out of the picture. (I believe that this was 126 in 3.3, > but is changing to "unlimited" based on Jan Beulich''s recent work. Is > that correct?)The default build configuration is for 64 CPUs. You have to re-build Xen to configure support for more CPUs than that. Yes, 126 is the limit for 3.3.> (2a) What''s the largest host memory that anybody has tested? > (2b) What''s the expected host memory limit (if somebody was able to > configure a system that large)?I think 256GB has been tested. Theoretically we''re good up to 1TB, and we could expand beyond even that without too much trouble.> (3a) What''s the largest guest memory that anybody has tested? > (3b) What''s the expected guest memory limit (if somebody was able to > configure a system that large)?I think 64GB guests are tested fairly often. There''s no particular reason that a guest couldn''t use all available memory, whatever that is (except for 32-bit PV guests which are limited for arcane technical reasons).> (4a) Does Xen support hot-add of physical hardware to the host system? > If so, which devices? > (4b) Hot remove?Depends what the usage scenario of those devices is. One answer would be that Xen supports device hotplug as far as dom0 supports it.> (5a) What''s the maximum # of virtual NICs per guest? > (5b) What''s the maximum # of virtual HBAs per guest? > (5c) What''s the maximum # of LUNs per guest? > (6) What''s the maximum # of powered-on guests per system?Theoretically only limited by available resources. I don''t know what''s actually been tested. -- Keir _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
Jan Beulich
2008-Nov-07 14:30 UTC
Re: [Xen-devel] Questions about certain Xen limits and features
>>> Keir Fraser <keir.fraser@eu.citrix.com> 07.11.08 15:22 >>> >> (2a) What''s the largest host memory that anybody has tested? >> (2b) What''s the expected host memory limit (if somebody was able to >> configure a system that large)? > >I think 256GB has been tested. Theoretically we''re good up to 1TB, and we >could expand beyond even that without too much trouble.1Tb has been tested recently by IBM. However, giving anything beyond 512Gb to Dom0 (or any other domain) is expected have issues, unless the kernel used is one that has fixes to deal with that (the patch I had submitted for that apparently caused some trouble in the 2.6.18 tree). The tools also aren''t prepared to deal with DomU-s larger than 512Gb, I believe. Jan _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
Vessey, Bruce A
2008-Nov-07 15:40 UTC
RE: [Xen-devel] Questions about certain Xen limits and features
Thanks. -----Original Message----- From: xen-devel-bounces@lists.xensource.com [mailto:xen-devel-bounces@lists.xensource.com] On Behalf Of Jan Beulich Sent: Friday, November 07, 2008 9:31 AM To: Keir Fraser; Vessey, Bruce A Cc: xen-devel@lists.xensource.com Subject: Re: [Xen-devel] Questions about certain Xen limits and features>>> Keir Fraser <keir.fraser@eu.citrix.com> 07.11.08 15:22 >>> >> (2a) What''s the largest host memory that anybody has tested? >> (2b) What''s the expected host memory limit (if somebody was able to >> configure a system that large)? > >I think 256GB has been tested. Theoretically we''re good up to 1TB, and >we could expand beyond even that without too much trouble.1Tb has been tested recently by IBM. However, giving anything beyond 512Gb to Dom0 (or any other domain) is expected have issues, unless the kernel used is one that has fixes to deal with that (the patch I had submitted for that apparently caused some trouble in the 2.6.18 tree). The tools also aren''t prepared to deal with DomU-s larger than 512Gb, I believe. Jan _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
Stefan de Konink
2008-Nov-10 01:51 UTC
Re: [Xen-devel] Questions about certain Xen limits and features
Keir Fraser wrote:>> (2a) What''s the largest host memory that anybody has tested? >> (2b) What''s the expected host memory limit (if somebody was able to >> configure a system that large)? > > I think 256GB has been tested. Theoretically we''re good up to 1TB, and we > could expand beyond even that without too much trouble.I have seen *very* weird bugs related to kernel error reporting when I made the switch from 16GB to 32GB of memory. I can do this ''semi'' dynamically using a Dell 1950. To be able to actually boot system with 32GB I have to append; i8042.noaux Might be good reference for other people. Stefan _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel