Hello guys,
We are currently testing Ceph Jewel with object-map feature enabled:
rbd image 'disk-22920':
size 102400 MB in 25600 objects
order 22 (4096 kB objects)
block_name_prefix: rbd_data.7cfa2238e1f29
format: 2
features: layering, exclusive-lock, object-map, fast-diff, deep-flatten
flags:
We use this RBD as disk for a kvm virtual machine with virtio-scsi and
discard=unmap. We noticed the following paremeters in /sys/block:
# cat /sys/block/sda/queue/discard_*
4096
1073741824
0 <- discard_zeroes_data
While trying to do a mkfs.ext4 on the disk in VM we noticed a low
performance with using discard.
mkfs.ext4 -E nodiscard /dev/sda1 - tooks 5 seconds to complete
mkfs.ext4 -E discard /dev/sda1 - tooks around 3 monutes
When disabling the object-map the mkfs with discard tooks just 5
seconds.
Do you have any idea what might cause this issue?
Kernel: 4.2.0-35-generic #40~14.04.1-Ubuntu
Ceph: 10.2.0
Libvirt: 1.3.1
QEMU: 2.5.0
Thanks!
Best regards,
Jonas
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