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The ungleich ceph handbook » History » Version 30

Nico Schottelius, 09/10/2020 02:30 PM

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h1. The ungleich ceph handbook
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{{toc}}
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h2. Status
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This document is **IN PRODUCTION**.
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h2. Introduction
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This article describes the ungleich storage architecture that is based on ceph. It describes our architecture as well maintenance commands. Required for 
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h2. Communication guide
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Usually when disks fails no customer communication is necessary, as it is automatically compensated/rebalanced by ceph. However in case multiple disk failures happen at the same time, I/O speed might be reduced and thus customer experience impacted.
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For this reason communicate whenever I/O recovery settings are temporarily tuned.
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h2. Analysing 
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h3. ceph osd df tree
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Using @ceph osd df tree@ you can see not only the disk usage per OSD, but also the number of PGs on an OSD. This is especially useful to see how the OSDs are balanced.
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h3. Find out the device of an OSD
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Use @mount | grep /var/lib/ceph/osd/ceph-OSDID@ on the server on which the OSD is located:
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<pre>
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[16:01:23] server2.place6:~# mount | grep /var/lib/ceph/osd/ceph-31
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/dev/sdk1 on /var/lib/ceph/osd/ceph-31 type xfs (rw,relatime,attr2,inode64,noquota)
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</pre>
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h2. Adding a new disk/ssd to the ceph cluster
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write on the disks, which order / date we bought it with a permanent marker.
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h3. For Dell servers
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First find the disk and then add it to the operating system
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<pre>
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megacli -PDList -aALL  | grep -B16 -i unconfigur
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# Sample output:
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[19:46:50] server7.place6:~#  megacli -PDList -aALL  | grep -B16 -i unconfigur
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Enclosure Device ID: N/A
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Slot Number: 0
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Enclosure position: N/A
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Device Id: 0
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WWN: 0000000000000000
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Sequence Number: 1
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Media Error Count: 0
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Other Error Count: 0
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Predictive Failure Count: 0
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Last Predictive Failure Event Seq Number: 0
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PD Type: SATA
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Raw Size: 894.252 GB [0x6fc81ab0 Sectors]
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Non Coerced Size: 893.752 GB [0x6fb81ab0 Sectors]
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Coerced Size: 893.75 GB [0x6fb80000 Sectors]
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Sector Size:  0
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Firmware state: Unconfigured(good), Spun Up
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</pre>
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Then add the disk to the OS:
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<pre>
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megacli -CfgLdAdd -r0 [Enclosure Device ID:slot] -aX (X : host is 0. md-array is 1)
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# Sample call, if enclosure and slot are KNOWN (aka not N/A)
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megacli -CfgLdAdd -r0 [32:0] -a0
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# Sample call, if enclosure is N/A
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megacli -CfgLdAdd -r0 [:0] -a0
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</pre>
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Then check disk
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<pre>
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fdisk -l
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[11:26:23] server2.place6:~# fdisk -l
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Disk /dev/sdh: 7.3 TiB, 8000987201536 bytes, 15626928128 sectors
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Units: sectors of 1 * 512 = 512 bytes
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Sector size (logical/physical): 512 bytes / 512 bytes
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I/O size (minimum/optimal): 512 bytes / 512 bytes
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[11:27:24] server2.place6:~#
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</pre>
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Then create gpt
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<pre>
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/opt/ungleich-tools/disk-create-fresh-gpt /dev/XXX
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[11:31:10] server2.place6:~# /opt/ungleich-tools/disk-create-fresh-gpt /dev/sdh
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Created a new DOS disklabel with disk identifier 0x9c4a0355.
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Command (m for help): Created a new GPT disklabel (GUID: 374E31AD-7B96-4837-B5ED-7B22C452899E).
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......
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</pre>
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Then create osd for ssd/hdd-big
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<pre>
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/opt/ungleich-tools/ceph-osd-create-start /dev/XXX XXX(sdd or hdd-big)
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[11:33:58] server2.place6:~# /opt/ungleich-tools/ceph-osd-create-start /dev/sdh hdd-big
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+ set -e
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+ [ 2 -lt 2 ]
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......
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+ /opt/ungleich-tools/monit-ceph-create-start osd.14
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osd.14
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[ ok ] Restarting daemon monitor: monit.
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[11:36:14] server2.place6:~#
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</pre>
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Then check rebalancing(if you want to add another disk, you should do after rebalancing)
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<pre>
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ceph -s
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[12:37:57] server2.place6:~# ceph -s
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  cluster:
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    id:     1ccd84f6-e362-4c50-9ffe-59436745e445
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    health: HEALTH_WARN
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            2248811/49628409 objects misplaced (4.531%)
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......
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  io:
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    client:   170KiB/s rd, 35.0MiB/s wr, 463op/s rd, 728op/s wr
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    recovery: 27.1MiB/s, 6objects/s
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[12:49:41] server2.place6:~#
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</pre>
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h2. Moving a disk/ssd to another server
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(needs to be described better)
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Generally speaking:
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* //needs to be tested: disable recovery so data wont start move while you have the osd down
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* /opt/ungleich-tools/ceph-osd-stop-disable does the following:
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** Stop the osd, remove monit on the server you want to take it out
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** umount the disk
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* Take disk out
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* Discard preserved cache on the server you took it out 
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** using megacli:  @megacli -DiscardPreservedCache -Lall -a0@
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* Insert into new server
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* Clear foreign configuration
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** using megacli: @megacli -CfgForeign -Clear -a0@
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* Disk will now appear in the OS, ceph/udev will automatically start the OSD (!)
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** No creating of the osd required!
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* Verify that the disk exists and that the osd is started
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** using *ps aux*
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** using *ceph osd tree*
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* */opt/ungleich-tools/monit-ceph-create-start osd.XX* # where osd.XX is the osd + number
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** Creates the monit configuration file so that monit watches the OSD
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** Reload monit
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* Verify monit using *monit status*
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h2. Removing a disk/ssd
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To permanently remove a failed disk from a cluster, use ***ceph-osd-stop-remove-permanently*** from ungleich-tools repo. Warning: if the disk is still active, the OSD will be shutdown AND removed from the cluster -> all data of that disk will need to be rebalanced.
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h2. Handling DOWN osds with filesystem errors
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If an email arrives with the subject "monit alert -- Does not exist osd.XX-whoami", the filesystem of an OSD cannot be read anymore. It is very highly likely that the disk / ssd is broken. Steps that need to be done:
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* Login to any ceph monitor (cephX.placeY.ungleich.ch)
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* Check **ceph -s**, find host using **ceph osd tree**
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* Login to the affected host
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* Run the following commands:
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** ls /var/lib/ceph/osd/ceph-XX
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** dmesg
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<pre>
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ex) After checking message of dmesg, you can do next step
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[204696.406756] XFS (sdl1): metadata I/O error: block 0x19100 ("xlog_iodone") error 5 numblks 64
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[204696.408094] XFS (sdl1): xfs_do_force_shutdown(0x2) called from line 1233 of file /build/linux-BsFdsw/linux-4.9.65/fs/xfs/xfs_log.c.  Return address = 0xffffffffc08eb612
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[204696.410702] XFS (sdl1): Log I/O Error Detected.  Shutting down filesystem
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[204696.411977] XFS (sdl1): Please umount the filesystem and rectify the problem(
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</pre>
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* Create a new ticket in the datacenter light project
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** Subject: "Replace broken OSD.XX on serverX.placeY.ungleich.ch"
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** Add (partial) output of above commands
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** Use /opt/ungleich-tools/ceph-osd-stop-remove-permanently XX, where XX is the osd id, to remove the disk from the cluster
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** Remove the physical disk from the host, checkout if there is warranty on it and if yes
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*** Create a short letter to the vendor, including technical details a from above
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*** Record when you sent it in
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*** Put ticket into status waiting
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** If there is no warranty, dispose it
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h2. Change ceph speed for i/o recovery
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By default we want to keep I/O recovery traffic low to not impact customer experience. However when multiple disks fail at the same point, we might want to prioritise recover for data safety over performance.
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The default configuration on our servers contains:
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<pre>
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[osd]
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osd max backfills = 1
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osd recovery max active = 1
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osd recovery op priority = 2
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</pre>
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The important settings are *osd max backfills* and *osd recovery max active*, the priority is always kept low so that regular I/O has priority.
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To adjust the number of backfills *per osd* and to change the *number of threads* used for recovery, we can use on any node with the admin keyring:
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<pre>
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ceph tell osd.* injectargs '--osd-max-backfills Y'
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ceph tell osd.* injectargs '--osd-recovery-max-active X'
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</pre>
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where Y and X are the values that we want to use. Experience shows that Y=5 and X=5 doubles to triples the recovery performance, whereas X=10 and Y=10 increases recovery performance 5 times.
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h2. Debug scrub errors / inconsistent pg message
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From time to time disks don't save what they are told to save. Ceph scrubbing detects these errors and switches to HEALTH_ERR. Use *ceph health detail* to find out which placement groups (*pgs*) are affected. Usually a ***ceph pg repair <number>*** fixes the problem.
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If this does not help, consult https://ceph.com/geen-categorie/ceph-manually-repair-object/.
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h2. Move servers into the osd tree
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New servers have their buckets placed outside the **default root** and thus need to be moved inside.
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Output might look as follows:
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<pre>
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[11:19:27] server5.place6:~# ceph osd tree
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ID  CLASS   WEIGHT    TYPE NAME        STATUS REWEIGHT PRI-AFF 
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 -3           0.87270 host server5                             
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 41     ssd   0.87270     osd.41           up  1.00000 1.00000 
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 -1         251.85580 root default                             
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 -7          81.56271     host server2                         
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  0 hdd-big   9.09511         osd.0        up  1.00000 1.00000 
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  5 hdd-big   9.09511         osd.5        up  1.00000 1.00000 
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...
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</pre>
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Use **ceph osd crush move serverX root=default** (where serverX is the new server),
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which will move the bucket in the right place:
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<pre>
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[11:21:17] server5.place6:~# ceph osd crush move server5 root=default
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moved item id -3 name 'server5' to location {root=default} in crush map
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[11:32:12] server5.place6:~# ceph osd tree
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ID  CLASS   WEIGHT    TYPE NAME        STATUS REWEIGHT PRI-AFF 
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 -1         252.72850 root default                             
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...
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 -3           0.87270     host server5                         
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 41     ssd   0.87270         osd.41       up  1.00000 1.00000 
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</pre>
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h2. How to fix existing osds with wrong partition layout
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In the first version of DCL we used filestore/3 partition based layout.
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In the second version of DCL, including OSD autodection, we use bluestore/2 partition based layout.
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To convert, we delete the old OSD, clean the partitions and create a new osd:
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h3. Inactive OSD
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If the OSD is *not active*, we can do the following:
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* Find the OSD number: mount the partition and find the whoami file
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<pre>
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root@server2:/opt/ungleich-tools# mount /dev/sda2 /mnt/
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root@server2:/opt/ungleich-tools# cat /mnt/whoami 
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0
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root@server2:/opt/ungleich-tools# umount  /mnt/
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</pre>
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* Verify in the *ceph osd tree* that the OSD is on that server
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* Deleting the OSD
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** ceph osd crush remove $osd_name
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** ceph osd rm $osd_name
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Then continue below as described in "Recreating the OSD".
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h3. Remove Active OSD
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* Use /opt/ungleich-tools/ceph-osd-stop-remove-permanently OSDID to stop and remove the OSD
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* Then continue below as described in "Recreating the OSD".
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h3. Recreating the OSD
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* Create an empty partition table
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** fdisk /dev/sdX
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** g
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** w
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* Create a new OSD
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** /opt/ungleich-tools/ceph-osd-create-start /dev/sdX CLASS # use hdd, ssd, ... for the CLASS
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h2. How to fix unfound pg
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refer to https://redmine.ungleich.ch/issues/6388
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* Check health state 
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** ceph health detail
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* Check which server has that osd
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** ceph osd tree
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* Check which VM is running in server place
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** virsh list  
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* Check pg map
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** ceph osd map [osd pool] [VMID]
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* revert pg
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** ceph pg [PGID] mark_unfound_lost revert
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h2. Enabling per image RBD statistics for prometheus
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<pre>
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[20:26:57] red2.place5:~# ceph config set mgr mgr/prometheus/rbd_stats_pools "one,hdd"
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[20:27:57] black2.place6:~# ceph config set mgr mgr/prometheus/rbd_stats_pools "hdd,ssd"
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</pre>
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h2. S3 Object Storage
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h3. Introduction
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* See the "Red Hat manual":https://access.redhat.com/documentation/en-us/red_hat_ceph_storage/3/html/object_gateway_guide_for_red_hat_enterprise_linux/overview-rgw
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* The "ceph docs about object storage":https://docs.ceph.com/docs/mimic/radosgw/
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h3. Architecture
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* S3 requests are handled by a publicly accessible gateway, which also has access to the ceph cluster.
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* s3 buckets are usually 
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h3. Setting up S3 object storage on Ceph