[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-users] Poor disk io performance in domUs
Lets say we have 4 domU heavy utilized. What about providing physical disk to every domU to avoid sharing single disk among all guests? Will it help to have didecated disk per domU? Peter 2007/6/22, Petersson, Mats <Mats.Petersson@xxxxxxx>: > > > > -----Original Message----- > > From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx > > [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of > > Andrej Radonic > > Sent: 22 June 2007 10:41 > > To: xen-users@xxxxxxxxxxxxxxxxxxx > > Subject: RE: [Xen-users] Poor disk io performance in domUs > > > > Hi Mats, > > > > >> so far we measured separately in dom0 and in the mail-domU. > > >> > The 20 MB/s happen as soon as there is concurrent io from two > > >> > or more domUs. > > > > > > That would be a consequence of the two domains causing more > > > head-movement on the drive(s) than a single domain, so you get more > > > overhead. So if you get 50MB/s in a single domain, you > > don't get 25MB/s > > > in two parallel domains - you get a bit less. That's just what I'd > > > expect in this situation. [This is because the "disk" for > > each virtual > > > machine is in a different part of the disk, so each time the first > > > domain acesses the disk, it needs a (big) move of the > > read/write head, > > > and then another big move when the second domain accesses > > it's part of > > > the disk]. > > > > OK, I definitely agree, but I am still not sure about the extent of > > throughput degradation. > > > > I remeasured the setup. This is what I get using dd to write a large > > file to the disk: > > > > dd simultaneously in both dom0 = 170 MB/s > I take it you mean "two parallel 'dd' commands at the same time"? That > would still write to the same portion of disk (unless you specifically > choose different partitions?) > > If it's the same partition, then, althouth there is some head movement > involved, there will be less head movement than two domains that start > 10GB apart on a disk. Also, the filesystem driver in the Dom0 can > re-arrange the disk accesses to make fewer movements. > > > dd simultaneously in two domU = 34 MB/s > I take it this means two different DomU doing "dd"? > Is that 34 MB/s "total" (i.e. 17MB/s per domain) or per domain (68 MB/s > total)? > > > dd in a single dom0 = 120 MB/s > So this is "better" than half of 170 MB/s, agreed? So even in a single > domain, running parallel sessions reduce the performance. > > Note also that there is overhead in transferring from Dom0 to DomU and > the other way around. Even if this is fairly small, it's not possible to > ignore this. > > > > > Would you really say that one-third of io performance is what > > is to be > > expected? > > It's difficult to say - I'm just trying to give you some explanation to > what you're seeing. > > -- > Mats > > > > Thanks for your cooperation. > > Andrej > > interSales AG, Cologne/Germany > > > > _______________________________________________ > > Xen-users mailing list > > Xen-users@xxxxxxxxxxxxxxxxxxx > > http://lists.xensource.com/xen-users > > > > > > > > > > _______________________________________________ > Xen-users mailing list > Xen-users@xxxxxxxxxxxxxxxxxxx > http://lists.xensource.com/xen-users > _______________________________________________ Xen-users mailing list Xen-users@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-users
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