Some notes about MySQL and PostgreSQL. Ceph's Storage clustering and KVM virtualization. Programming with NodeJS and PHP. Hacking with RaspberryPI and Arduino.
Actually your server is working hard managing multiple attempts to login, especially in such frameworks like
Wordpress and Joomla. The saturation of database connections results in Denial-of-Service and the website downtimes!
To block the unsolicited requests and avoid website downtimes we just need to follow some steps
Nowadays we inherit a lot of old databases.
The typical problem is to extract data from badly encoded fields.
This happens when the browser encoding is forced to let say UTF8
and MySQL is accepting the the default LATIN1 encoding. In this case
the problem does not manifests immediately since the byte sequence corresponding to
the single character remains immute during the saving and retrieval, but become a problem
when dumped and migrated.
Lets get workaround this problem. At first find non ASCII characters in the dump file
If you ever woundered why your 10Gbit link on Proxmox node is used only by a few percent during the migration, so you came to the right place.
The main reason is the security measures taken to protect virtual machine memory during the migration. All volume of memory will be transmitted via secure tunnel and that penalizes the speed:
Nov 24 12:26:41 starting migration of VM 123 to node 'proxmox1'(10.0.1.1)
Nov 24 12:26:41 copying disk images
Nov 24 12:26:41 starting VM 123 on remote node 'proxmox1'
Nov 24 12:26:43 starting ssh migration tunnel
Nov 24 12:26:43 starting online/live migration on localhost:60000
Nov 24 12:26:43 migrate_set_speed: 8589934592
Nov 24 12:26:43 migrate_set_downtime: 0.1
Nov 24 12:26:45 migration status: active (transferred 133567908, remaining 930062336), total 1082789888)
Nov 24 12:26:47 migration status: active (transferred 273781779, remaining 788221952), total 1082789888)
...
Nov 24 12:26:58 migration status: active (transferred 1036346176, remaining 20889600), total 1082789888)
Nov 24 12:26:58 migration status: active (transferred 1059940218, remaining 11558912), total 1082789888)
Nov 24 12:26:59 migration speed: 64.00 MB/s - downtime 54 ms
Nov 24 12:26:59 migration status: completed
Nov 24 12:27:02 migration finished successfuly (duration 00:00:21)
TASK OK
If your configured your Proxmox cluster to use the dedicated network isolated from the public one so you may low down the security level
Nov 24 12:42:19 starting migration of VM 100 to node 'proxmox2'(10.0.1.2)
Nov 24 12:42:19 copying disk images
Nov 24 12:42:19 starting VM 100 on remote node 'proxmox2'
Nov 24 12:42:35 starting ssh migration tunnel
Nov 24 12:42:36 starting online/live migration on 10.0.1.2:60000
Nov 24 12:42:36 migrate_set_speed: 8589934592
Nov 24 12:42:36 migrate_set_downtime: 0.1
Nov 24 12:42:38 migration status: active (transferred 728684636, remaining 5655494656), total 6451433472)
Nov 24 12:42:40 migration status: active (transferred 1465523175, remaining 4865253376), total 6451433472)
....
Nov 24 12:42:55 migration status: active (transferred 7115710846, remaining 69742592), total 6451433472)
Nov 24 12:42:55 migration speed: 323.37 MB/s - downtime 262 ms
Nov 24 12:42:55 migration status: completed
Nov 24 12:42:58 migration finished successfuly (duration 00:00:39)
TASK OK
now you’re using all available bandwidth for migration, that also is very useful during migration heavy loaded instances.
Today we discuss how to manage wisely your cache setting in Ceph (ceph.com/docs/master/rbd/rbd-config-ref/). The type of cache discussed below is the user space implementation of the Ceph block device (i.e., librbd).
Suddenly after migration to Ceph we start observing the doubling of memory usage by every virtual machine.
After some research we found the configuration error in ceph.conf. The option rbd cache size describes the amount of cache reserved for every virtual disk, so the total amount of RAM reserved for cache is given by
total amount of ram =(number of virtual disks) X (rbd cache size)
After some rational reasoning of the kind - the standard hard drive usually possess 64M of cache - the final version of configuration will be the following
rbd cache =true
rbd cache size = 67108864 # (64MB)
rbd cache max dirty = 50331648 # (48MB)
rbd cache target dirty = 33554432 # (32MB)
rbd cache max dirty age = 2
rbd cache writethrough until flush =true
To apply settings without virtual machine restart use KVM live migration. After the virtual machine is migrated from host1 to host2 the new process will start taking into account the modification to the ceph configuration.
If not sure about setting leave Ceph’s default values for amount of cache, simply enable it
rbd cache =true
rbd cache writethrough until flush =true
Choose a disk with the most optimal ratio IOPS/price. Check out the list of disks in order of IOPS (Input/Output Operations Per Second) performance: en.wikipedia.org/wiki/IOPS.
Quite often SSD disks are released with firmware bugs or with non-optimal configurations, so before putting the system in production checkout the latest version.
$ sudo hdparm -I /dev/sda | grep-i trim
* Data Set Management TRIM supported (limit 8 blocks)
It is very important to have TRIM functioning. Without TRIM the disk speed will degrade with time due to the fact that the SSD will have to erase the cell before every write operation.
Let’s test it simply by executing fstrim
$ sudo fstrim -v /
/: 98147174400 bytes were trimmed
Lets test whether the TRIM is really doing what it should
