2007-11-01 20:36:06 UTC
I've got Solaris Express Community Edition build 75 (75a) installed on an Asus P5K-E/WiFI-AP (ip35/ICH9R based) board. CPU=Q6700, RAM=8Gb, disk=Samsung HD501LJ and (older) Maxtor 6H500F0.
When the O/S is running on bare metal, ie no xVM/Xen hypervisor, then everything is fine.
When it's booted up running xVM and the hypervisor, then unlike plain disk I/O, and unlike svm volumes, zfs is around 20 time slower.
Specifically, with either a plain ufs on a raw/block disk device, or ufs on a svn meta device, a command such as dd if=/dev/zero of=2g.5ish.dat bs=16k count=150000 takes less than a minute, with an I/O rate of around 30-50Mb/s.
Similary, when running on bare metal, output to a zfs volume, as reported by zpool iostat, shows a similar high output rate. (also takes less than a minute to complete).
But, when running under xVM and a hypervisor, although the ufs rates are still good, the zfs rate drops after around 500Mb.
For instance, if a window is left running zpool iostat 1 1000, then after the "dd" command above has been run, there are about 7 lines showing a rate of 70Mbs, then the rate drops to around 2.5Mb/s until the entire file is written. Since the dd command initially completes and returns control back to the shell in around 5 seconds, the 2 gig of data is cached and is being written out. It's similar with either the Samsung or Maxtor disks (though the Samsung are slightly faster).
Although previous releases running on bare metal (with xVM/Xen) have been fine, the same problem exists with the earlier b66-0624-xen drop of Open Solaris
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