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[Xen-users] 4KB Sector Disks

I just thought I'd mention this because it turned out to be the cause of disk I/O performance issues I've been having. For the arhchive/search engines of nothing else.


Storage server (Linux):
1) ZFS zvol backed images, ZFS configured for 4KB sector disks
2) IETD iSCSI server

dom0 (Linux):
3) Open-iSCSI client (Linux)

domU is Windows.

When 2) is set for 4096 byte sectors, the performance is terrible, and qemu-dm tops out at about 5MB/s when it hits the CPU limit. Reduce it to 512 bytes, re-partition accordingly to ensure the partition is 4KB aligned, and the performance goes up massively. Booting up domU now takes seconds rather than minutes, and doing the fresh-install-millions-of-updates update takes minutes rather than hours.

Something in the stack really seems to grind to a halt when dealing with 4KB physical sectors at the moment. Nothing breaks or warns, it just runs really slowly.


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