Hi Stefan,
that's not 100% pure experiment. Fresh OSD might be faster by itself.
E.g. due to lack of space fragmentation and/or empty lookup tables.
You might want to recreate OSD.0 without DB and attach DB manually. Then
benchmark resulting OSD.
Different experiment if you have another slow OSD with recently added DB
would be to:
Compare benchmark results for both bitmap and stupid allocators for this
specific OSD. I.e. benchmark it as-is then change
bluestore_allocator/bluefs_allocator to stupid and benchmark again.
And just in case - I presume all the benchmark results are persistent,
i.e. you can see the same results for multiple runs.
Thanks,
Igor
On 4/24/2020 12:32 PM, Stefan Priebe - Profihost AG wrote:
Hi Igor,
there must be a difference. I purged osd.0 and recreated it.
Now it gives:
ceph tell osd.0 bench
{
"bytes_written": 1073741824,
"blocksize": 4194304,
"elapsed_sec": 8.1554735639999993,
"bytes_per_sec": 131659040.46819863,
"iops": 31.389961354303033
}
What's wrong wiht adding a block.db device later?
Stefan
Am 23.04.20 um 20:34 schrieb Stefan Priebe - Profihost AG:
Hi,
if the OSDs are idle the difference is even more worse:
# ceph tell osd.0 bench
{
"bytes_written": 1073741824,
"blocksize": 4194304,
"elapsed_sec": 15.396707875000001,
"bytes_per_sec": 69738403.346825853,
"iops": 16.626931034761871
}
# ceph tell osd.38 bench
{
"bytes_written": 1073741824,
"blocksize": 4194304,
"elapsed_sec": 6.8903985170000004,
"bytes_per_sec": 155831599.77624846,
"iops": 37.153148597776521
}
Stefan
Am 23.04.20 um 14:39 schrieb Stefan Priebe - Profihost AG:
Hi,
Am 23.04.20 um 14:06 schrieb Igor Fedotov:
I don't recall any additional tuning to be applied to new DB
volume. And assume the hardware is pretty the same...
Do you still have any significant amount of data spilled over for
these updated OSDs? If not I don't have any valid explanation for
the phenomena.
just the 64k from here:
https://tracker.ceph.com/issues/44509
You might want to try "ceph osd bench" to compare OSDs under pretty
the same load. Any difference observed
Servers are the same HW. OSD Bench is:
# ceph tell osd.0 bench
{
"bytes_written": 1073741824,
"blocksize": 4194304,
"elapsed_sec": 16.091414781000001,
"bytes_per_sec": 66727620.822242722,
"iops": 15.909104543266945
}
# ceph tell osd.36 bench
{
"bytes_written": 1073741824,
"blocksize": 4194304,
"elapsed_sec": 10.023828538,
"bytes_per_sec": 107118933.6419194,
"iops": 25.539143953780986
}
OSD 0 is a Toshiba MG07SCA12TA SAS 12G
OSD 36 is a Seagate ST12000NM0008-2H SATA 6G
SSDs are all the same like the rest of the HW. But both drives
should give the same performance from their specs. The only other
difference is that OSD 36 was directly created with the block.db
device (Nautilus 14.2.7) and OSD 0 (14.2.8) does not.
Stefan
On 4/23/2020 8:35 AM, Stefan Priebe - Profihost AG wrote:
Hello,
is there anything else needed beside running:
ceph-bluestore-tool --path /var/lib/ceph/osd/ceph-${OSD}
bluefs-bdev-new-db --dev-target /dev/vgroup/lvdb-1
I did so some weeks ago and currently i'm seeing that all osds
originally deployed with --block-db show 10-20% I/O waits while
all those got converted using ceph-bluestore-tool show 80-100% I/O
waits.
Also is there some tuning available to use more of the SSD? The
SSD (block-db) is only saturated at 0-2%.
Greets,
Stefan
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