Apache CloudStack and MySQL 5.7

SQL Mode

Starting with MySQL 5.7 the default SQL mode is far more strict then it was before.

It now includes ONLY_FULL_GROUP_BY, STRICT_TRANS_TABLES, NO_ZERO_IN_DATE, NO_ZERO_DATE, ERROR_FOR_DIVISION_BY_ZERO, NO_AUTO_CREATE_USER, and NO_ENGINE_SUBSTITUTION.

This can cause problems for applications which need other SQL modes. Apache CloudStack is one of these applications.

The best thing would be to modify the SQL queries executed by CloudStack, but that’s not that easy.

Changing the mode

Luckily the SQL mode can be changed in either the my.conf or as a session variable.

In the my.cnf one can add:

[mysqld]
sql_mode = 'STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION'

Or modify the /etc/cloudstack/management/db.properties file to include this line:

db.cloud.url.params=prepStmtCacheSize=517&cachePrepStmts=true&sessionVariables=sql_mode='STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION'

You should now be able to run a CloudStack management server on MySQL 5.7!

Future

In the future CloudStack should only be using SQL queries which comply with the new more strict SQL mode. In the meantine a issue and Pull Request have been created to track this situation.

Do not use SMR disks with Ceph

Many new disks like the Seagate He8 disks are using a technique called Shingled Magnetic Recording to increase capacity.

As these disks offer a very low price per Gigabyte they seem interesting to use in a Ceph cluster.

Performance

Due to the nature of SMR these disks are very, very, very bad when it comes to Random Write performance. Random I/O is something that Ceph does a lot on the backing disks.

This results in disks spiking to 100% utilization very quickly causing all kinds of trouble with OSDS going down and committing suicide.

Do NOT use them

The solution is very simple. Do not use SMR disks in Ceph but stick to the traditional PMR disks in your Ceph cluster.

In the future we might see SMR support in the new BlueStore of Ceph, but at this moment no work has been done, so don’t expect anything soon.

Testing Ceph BlueStore with the Kraken release

Ceph version Kraken (11.2.0) has been released and the Release Notes tell us that the new BlueStore backend for the OSDs is now available.

BlueStore

The current backend for the OSDs is the FileStore which mainly uses the XFS filesystem to store it’s data. To overcome several limitations of XFS and POSIX in general the BlueStore backend was developed.

It will provide more performance (mainly writes), data safety due to checksumming and compression.

Users are encouraged to test BlueStore starting with the Kraken release for non-production and non-critical data sets and report back to the community.

Deploying with BlueStore

To deploy OSDs with BlueStore you can use the ceph-deploy by using the –bluestore flag.

I created a simple test cluster with three machines: alpha, bravo and charlie.

Each machine will be running a ceph-mon and ceph-osd proces.

This is the sequence of ceph-deploy commands I used to deploy the cluster

ceph-deploy new alpha bravo charlie
ceph-deploy mon create alpha bravo charlie

Now, edit the ceph.conf file in the current directory and add:

[osd]
enable_experimental_unrecoverable_data_corrupting_features = bluestore

With this setting we allow the use of BlueStore and we can now deploy our OSDs:

ceph-deploy --overwrite-conf osd create --bluestore alpha:sdb bravo:sdb charlie:sdb

Running BlueStore

This tiny cluster how runs three OSDs with BlueStore:

root@alpha:~# ceph -s
    cluster c824e460-2f09-4994-8b2f-108aedc52d19
     health HEALTH_OK
     monmap e2: 3 mons at {alpha=[2001:db8::100]:6789/0,bravo=[2001:db8::101]:6789/0,charlie=[2001:db8::102]:6789/0}
            election epoch 14, quorum 0,1,2 alpha,bravo,charlie
        mgr active: charlie standbys: alpha, bravo
     osdmap e14: 3 osds: 3 up, 3 in
            flags sortbitwise,require_jewel_osds,require_kraken_osds
      pgmap v24: 64 pgs, 1 pools, 0 bytes data, 0 objects
            43356 kB used, 30374 MB / 30416 MB avail
                  64 active+clean
root@alpha:~#

root@alpha:~# ceph osd tree
ID WEIGHT  TYPE NAME        UP/DOWN REWEIGHT PRIMARY-AFFINITY 
-1 0.02907 root default                                       
-2 0.00969     host alpha                                     
 0 0.00969         osd.0         up  1.00000          1.00000 
-3 0.00969     host bravo                                     
 1 0.00969         osd.1         up  1.00000          1.00000 
-4 0.00969     host charlie                                   
 2 0.00969         osd.2         up  1.00000          1.00000 
root@alpha:~#

On alpha I see that osd.0 only has a small partition for a bit of configuration and the rest is used by BlueStore.

root@alpha:~# df -h /var/lib/ceph/osd/ceph-0
Filesystem      Size  Used Avail Use% Mounted on
/dev/sdb1        97M  5.4M   92M   6% /var/lib/ceph/osd/ceph-0
root@alpha:~# lsblk 
NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda      8:0    0    8G  0 disk 
├─sda1   8:1    0  7.5G  0 part /
├─sda2   8:2    0    1K  0 part 
└─sda5   8:5    0  510M  0 part [SWAP]
sdb      8:16   0   10G  0 disk 
├─sdb1   8:17   0  100M  0 part /var/lib/ceph/osd/ceph-0
└─sdb2   8:18   0  9.9G  0 part 
sdc      8:32   0   10G  0 disk 
root@alpha:~# cat /var/lib/ceph/osd/ceph-0/type
bluestore
root@alpha:~#

The OSDs should work just like OSDs running FileStore, but they should perform better.