June 25, 2010, 12:31 pm
If you’re have a hardware RAID controller using mptsas module on your Linux server, you may notice your write performance is extremely poor – i.e. some database workloads can be 30x slower than on other servers (i.e. using Linux software RAID).
An example card below – lspci shows:
02:05.0 SCSI storage controller: LSI Logic / Symbios Logic SAS1068 PCI-X Fusion-MPT SAS (rev 01)
How can you fix it? See below.
Continue reading ‘poor write performance on Fusion MPT SAS RAID controllers’ »
May 26, 2010, 4:18 pm
There are some tasks in qemu / kvm monitor which could be scripted (i.e. like changing VNC password on demand).
Here is how.
Continue reading ‘Scripting qemu / kvm monitor’ »
May 11, 2010, 11:30 pm
Ever seen this message in your /proc/mdstat right after you boot the server and wondered what it is?
Continue reading ‘md0 : active (auto-read-only) in /proc/mdadm’ »
April 6, 2010, 11:38 pm
Sometimes, you will see MySQL setups where only one database is being replicated. How to add a second database, so that it’s also replicated?
Continue reading ‘MySQL replication: adding a new database’ »
February 27, 2010, 12:26 am
CentOS 5.x comes with PHP 5.1, which is too old for some applications.
Here is a quickie on how to update it using CentOS development / testing repository.
Continue reading ‘CentOS – update / install PHP 5.2’ »
April 23, 2009, 1:19 pm
Do you have a netbook, laptop, desktop or a server which uses dm-crypt to encrypt data on your disks? If yes, you will probably find that raw hard disk performance is better than encrypted disk performance. You will notice that especially on slow machines (i.e. netbooks), but also high-performance servers, because of the current dm-crypt design.
What cipher in the Linux kernel provides you with the best performance?
Continue reading ‘Cipher benchmark for dm-crypt / LUKS’ »
March 28, 2009, 1:17 am
Was your mail ever rejected or tagged as spam because it didn’t have a DKIM signature? You could enable DKIM-signing in Exim, but then, some older mail systems may still use DomainKeys.
Currently, Exim does not support signing mails with both DomainKeys and DKIM. You have to pick one of them, unless you do some tricks with patching Exim or connecting back to itself.
Still though, such setup is not perfect: Exim does not wrap its DomainKeys signature, which may result in SpamAssassin installations tagging your mail with HEAD_LONG rule (“Message headers are very long”) and assigning it 2.5 spam points.
So how to sign mail with DKIM and DomainKeys without negative consequences of being tagged by SpamAssassin for very long headers? DKIMproxy to the rescue!
Exim configuration
Continue reading ‘Setting up DKIMproxy with Exim for DKIM and DomainKeys signing’ »
August 27, 2008, 8:16 pm
Recently I was setting up DRBD (in short: “block devices designed as a building block to form high availability (HA) clusters”) between two data centers.
DRBD doesn’t apply any form of compression on the data that is replicated; is it a good idea to enable compression in the VPN link if you replicate your data with DRBD over Internet? Here is a quick test.
Continue reading ‘DRDB and link compression’ »
July 21, 2008, 10:17 pm
Do you happen to be running a Linux distribution and have Panasonic Lumix digital camera?
If yes, you may have problems downloading photos from it – depending on your kernel and udev settings, or more generally, on Linux distribution used.
The tips from below may help you.
Continue reading ‘Linux and Lumix digital cameras’ »