FWIW, Igor has been doing some great work on improving performance with
the 4k_min_alloc size. He gave a presentation at a recent weekly
performance meeting on it and it's looking really good. On HDDs I think
he was seeing up to 2X faster 8K-128K random writes at the expense of up
to a 20% sequential read hit when there is fragmentation all while
retaining the space saving benefits of the 4K min_alloc size. I believe
in a future point release we should be able to have 4K be the default
for both HDD and flash as it's already arguably faster on NVMe at this
point.
Mark
On 3/24/20 12:03 PM, Steven Pine wrote:
Hi Vitaliy,
You may be coming across the EC space amplification issue,
https://tracker.ceph.com/issues/44213
I am not aware of any recent updates to resolve this issue.
Sincerely,
On Tue, Mar 24, 2020 at 12:53 PM <vitalif@xxxxxxxxxx> wrote:
Hi.
I'm experiencing some kind of a space leak in Bluestore. I use EC,
compression and snapshots. First I thought that the leak was caused by
"virtual clones" (issue #38184). However, then I got rid of most of the
snapshots, but continued to experience the problem.
I suspected something when I added a new disk to the cluster and free
space in the cluster didn't increase (!).
So to track down the issue I moved one PG (34.1a) using upmaps from
osd11,6,0 to osd6,0,7 and then back to osd11,6,0.
It ate +59 GB after the first move and +51 GB after the second. As I
understand this proves that it's not #38184. Devirtualizaton of virtual
clones couldn't eat additional space after SECOND rebalance of the same
PG.
The PG has ~39000 objects, it is EC 2+1 and the compression is enabled.
Compression ratio is about ~2.7 in my setup, so the PG should use ~90 GB
raw space.
Before and after moving the PG I stopped osd0, mounted it with
ceph-objectstore-tool with debug bluestore = 20/20 and opened the
34.1a***/all directory. It seems to dump all object extents into the log
in that case. So now I have two logs with all allocated extents for osd0
(I hope all extents are there). I parsed both logs and added all
compressed blob sizes together ("get_ref Blob ... 0x20000 -> 0x...
compressed"). But they add up to ~39 GB before first rebalance
(34.1as2), ~22 GB after it (34.1as1) and ~41 GB again after the second
move (34.1as2) which doesn't indicate a leak.
But the raw space usage still exceeds initial by a lot. So it's clear
that there's a leak somewhere.
What additional details can I provide for you to identify the bug?
I posted the same message in the issue tracker,
https://tracker.ceph.com/issues/44731
--
Vitaliy Filippov
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