[ceph-users] Hammer to Jewel Upgrade - Extreme OSD Boot Time

Chris Jones chris.jones at ctl.io
Wed Nov 1 10:04:24 PDT 2017


Greg,

Thanks so much for the reply!

We are not clear on why ZFS is behaving poorly under some circumstances on getxattr system calls, but that appears to be the case.

Since the last update we have discovered that back-to-back booting of the OSD yields very fast boot time, and very fast getxattr system calls.

A longer period between boots (or perhaps related to influx of new data) correlates to longer boot duration. This is due to slow getxattr calls of certain types.

We suspect this may be a caching or fragmentation issue with ZFS for xattrs. Use of longer filenames appear to make this worse.

We experimented on some OSDs with swapping over to XFS as the filesystem, and the problem does not appear to be present on those OSDs.

The two examples below are representative of a Long Boot (longer running time and more data influx between osd rebooting) and a Short Boot where we booted the same OSD back to back.

Notice the drastic difference in time on the getxattr that yields the ENODATA return. Around 0.009 secs for "long boot" and "0.0002" secs when the same OSD is booted back to back. Long boot time is approx 40x to 50x longer. Multiplied by thousands of getxattr calls, this is/was our source of longer boot time.

We are considering a full switch to XFS, but would love to hear any ZFS tuning tips that might be a short term workaround.

We are using ZFS 6.5.11 prior to implementation of the ability to use large dnodes which would allow the use of dnodesize=auto.

#Long Boot
<0.000044>[pid 3413902] 13:08:00.884238 getxattr("/osd/9/current/20.86bs3_head/default.34597.7\\uptboatonthewaytohavanaiusedtomakealivingmanpickinthebanananowimaguidefortheciahoorayfortheusababybabymakemelocobabybabymakememambosenttospyonacubantalentshowfirststophavanagogoiusedtomakealivingmanpickinthebana_1d9e1e82d623f49c994f_0_long", "user.cephos.lfn3", "default.34597.7\uptboatonthewaytohavanaiusedtomakealivingmanpickinthebanananowimaguidefortheciahoorayfortheusababybabymakemelocobabybabymakememambosenttospyonacubantalentshowfirststophavanagogoiusedtomakealivingmanpickinthebananahoorayforhavanababybabymakemelocobabybabymakememamboptboatonthewaytohavanaiusedtomakealivingmanpickinthebanananowimaguidefortheciahoorayfortheusababybabymakemelocobabybabymakememambosenttospyonacubantalentshowfirststophavanagogoiusedtomakealivingmanpickinthebananahoorayforhavanababybabymakemelocobabybabymakememambo-92d9df789f9aaf007c50c50bb66e70af__head_0177C86B__14_ffffffffffffffff_3", 1024) = 616 <0.000044>
<0.008875>[pid 3413902] 13:08:00.884476 getxattr("/osd/9/current/20.86bs3_head/default.34597.57\\uptboatonthewaytohavanaiusedtomakealivingmanpickinthebanananowimaguidefortheciahoorayfortheusababybabymakemelocobabybabymakememambosenttospyonacubantalentshowfirststophavanagogoiusedtomakealivingmanpickintheban_79a7acf2d32f4302a1a4_0_long", "user.cephos.lfn3-alt", 0x7f849bf95180, 1024) = -1 ENODATA (No data available) <0.008875>

#Short Boot
<0.000015> [pid 3452111] 13:37:18.604442 getxattr("/osd/9/current/20.15c2s3_head/default.34597.22\\uptboatonthewaytohavanaiusedtomakealivingmanpickinthebanananowimaguidefortheciahoorayfortheusababybabymakemelocobabybabymakememambosenttospyonacubantalentshowfirststophavanagogoiusedtomakealivingmanpickintheban_efb8ca13c57689d76797_0_long", "user.cephos.lfn3", "default.34597.22\uptboatonthewaytohavanaiusedtomakealivingmanpickinthebanananowimaguidefortheciahoorayfortheusababybabymakemelocobabybabymakememambosenttospyonacubantalentshowfirststophavanagogoiusedtomakealivingmanpickinthebananahoorayforhavanababybabymakemelocobabybabymakememamboptboatonthewaytohavanaiusedtomakealivingmanpickinthebanananowimaguidefortheciahoorayfortheusababybabymakemelocobabybabymakememambosenttospyonacubantalentshowfirststophavanagogoiusedtomakealivingmanpickinthebananahoorayforhavanababybabymakemelocobabybabymakememambo-b519f8607a3d9de0f815d18b6905b27d__head_9726F5C2__14_ffffffffffffffff_3", 1024) = 617 <0.000015>
<0.000018> [pid 3452111] 13:37:18.604546 getxattr("/osd/9/current/20.15c2s3_head/default.34597.66\\uptboatonthewaytohavanaiusedtomakealivingmanpickinthebanananowimaguidefortheciahoorayfortheusababybabymakemelocobabybabymakememambosenttospyonacubantalentshowfirststophavanagogoiusedtomakealivingmanpickintheban_0e6d86f58e03d0f6de04_0_long", "user.cephos.lfn3-alt", 0x7fd4e8017680, 1024) = -1 ENODATA (No data available) <0.000018>



--------------------------------------------------
Christopher J. Jones


________________________________
From: Gregory Farnum <gfarnum at redhat.com>
Sent: Monday, October 30, 2017 6:20:15 PM
To: Chris Jones
Cc: ceph-users at lists.ceph.com
Subject: Re: [ceph-users] Hammer to Jewel Upgrade - Extreme OSD Boot Time

On Thu, Oct 26, 2017 at 11:33 AM Chris Jones <chris.jones at ctl.io<mailto:chris.jones at ctl.io>> wrote:

The long running functionality appears to be related to clear_temp_objects(); from OSD.cc called from init().


What is this functionality intended to do? Is it required to be run on every OSD startup? Any configuration settings that would help speed this up?


This function looks like it's cleaning up temporary objects that might have been left behind. Basically, we are scanning through the objects looking for temporaries, but we stop doing so once we hit a non-temp object (implying they are ordered). So in the common case I think we're doing one listing in each PG, finding there are no temp objects (or noting the few that remain), and then advancing to the next PG. This will take a little time as we're basically doing one metadata listing per PG, but that should end quickly.

I'm curious why this is so slow for you as I'm not aware of anybody else reporting such issues. I suspect the ZFS backend is behaving rather differently than the others, or that you've changed the default config options dramatically, so that your OSDs have to do a much larger listing in order to return the sorted list the OSD interface requires.
-Greg
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