Platforms supported
- Intel® / AMD™ 32 bit Linux
- Intel® / AMD™ 64 bit Linux
- HP PA-RISC HP-UX® 10.20 and above
- Sun® SPARC Solaris™ 8 and above
- HP Alpha OpenVMS 7.2-1 and above
- SCO® OpenServer 5.0.5 and above
- Sun® Intel® Solaris™ 10 and above
- IBM AIX® 4.3 and above
- HP Integrity OpenVMS 8.2-1 and above
- HP Intel® Itanium® HP-UX® 11.23 and above
- Mac OS X leopard 10.5 and above
Large File Support is available for Windows, Itanium HP-UX and Linux.
Recital provides a wide variety of connectivity solutions to external data sources. This article provides an overview.
DRBD:
DRBD (Distributed Replicated Block Device) forms the storage redundancy portition of a HA cluster setup. Explained in basic terms DRBD provides a means of achieving RAID 1 behavoir over a network, where whole block devices are mirrored accross the network.
To start off you will need 2 indentically sized raw drives or partitions. Many how-to's on the internet assume the use of whole drives, of course this will be better performance, but if you are simply getting familar with the technology you can repartition existing drives to allow for two eqaully sized raw partitions, one on each of the systems you will be using.
There are 3 DRBD replication modes:
• Protocol A: Write I/O is reported as completed as soon as it reached local disk and local TCP send buffer
• Protocol B: Write I/O is reported as completed as soon as it reached local disk and remote TCP buffer cache
• Protocol C: Write I/O is reported as completed as soon as it reached both local and remote disks.
If we were installing the HA cluster on a slow LAN or if the geogrphical seperation of the systems involved was great, then I recommend you opt for asyncronous mirroring (Protocol A) where the notifcation of a completed write operation occurs as soon as the local disk write is performed. This will greatly improve performance.
As we are setting up our HA cluster connected via a fast LAN, we will be using DRBD in fully syncronous mode, protocol C.
Protocol C involves the file system on the active node only being notified that the write operation was finished when the block is written to both disks of the cluster. Protocol C is the most commonly used mode of DRBD.
/etc/drbd.conf
global { usage-count yes; }
common { syncer { rate 10M; } }
resource r0 {
protocol C;
net {
max-buffers 2048;
ko-count 4;
}
on bailey {
device /dev/drbd0;
disk /dev/sda4;
address 192.168.1.125:7789;
meta-disk internal;
}
on giskard {
device /dev/drbd0;
disk /dev/sda3;
address 192.168.1.127:7789;
meta-disk internal;
}
}
drbd.conf explained:
Global section, usage-count. The DRBD project keeps statistics about the usage of DRBD versions. They do this by contacting a HTTP server each time a new DRBD version is installed on a system. This can be disabled by setting usage-count no;.
The common seciton contains configurations inhereted by all resources defined.
Setting the syncronisation rate, this is accoimplished by going to the syncer section and then assigning a value to the rate setting. The syncronisation rate refers to rate in which the data is being mirrored in the background. The best setting for the syncronsation rate is related to the speed of the network with which the DRBD systems are communicating on. 100Mbps ethernet supports around 12MBps, Giggabit ethernet somewhere around 125MBps.
in the configuration above, we have a resource defined as r0, the nodes are configured in the "on" host subsections.
"Device" configures the path of the logical block device that will be created by DRBD
"Disk" configures the block device that will be used to store the data.
"Address" configures the IP address and port number of the host that will hold this DRBD device.
"Meta-disk" configures the location where the metadata about the DRBD device will be stored.
You can set this to internal and DRBD will use the physical block device to store the information, by recording the metadata within the last sections of the disk.
Once you have created your configuration file, you must conduct the following steps on both the nodes.
Create device metadata.
$ drbdadm create-md r0
v08 Magic number not found
Writing meta data...
initialising activity log
NOT initialized bitmap
New drbd meta data block sucessfully created.
success
Attach the backing device.
$ drbdadm attach r0
Set the syncronisation parameters.
$ drbdadm syncer r0
Connect it to the peer.
$ drbdadm connect r0
Run the service.
$ service drbd start
Heartbeat:
Heartbeat provides the IP redundancy and the service HA functionailty.
On the failure of the primary node the VIP is assigned to the secondary node and the services configured to be HA are started on the secondary node.
Heartbeat configuration:
/etc/ha/ha.conf
## /etc/ha.d/ha.cf on node1
## This configuration is to be the same on both machines
## This example is made for version 2, comment out crm if using version 1
// replace the node variables with the names of your nodes.
crm no
keepalive 1
deadtime 5
warntime 3
initdead 20
bcast eth0
auto_failback yes
node bailey
node giskard
/etc/ha.d/authkeys
// The configuration below set authentication off, and encryption off for the authentication of nodes and their packets.
//Note make sure the authkeys file has the correct permisisions chmod 600
## /etc/ha.d/authkeys
auth 1
1 crc
/etc/ha.d/haresources
//192.168.1.40 is the VIP (Virtual IP) assigned to the cluster.
//the "smb" in the configuration line represents the service we wish to make HA
// /devdrbd0 represents the resource name you configured in the drbd.conf
## /etc/ha.d/haresources
## This configuration is to be the same on both nodes
bailey 192.168.1.40 drbddisk Filesystem::/dev/drbd0::/drbdData::ext3 smb
DirectoryIndex default.rsp index.html
http://msdn.microsoft.com/en-us/library/cc351024(VS.85).aspx
After split brain has been detected, one node will always have the resource in a StandAlone connection state. The other might either also be in the StandAlone state (if both nodes detected the split brain simultaneously), or in WFConnection (if the peer tore down the connection before the other node had a chance to detect split brain).
At this point, unless you configured DRBD to automatically recover from split brain, you must manually intervene by selecting one node whose modifications will be discarded (this node is referred to as the split brain victim). This intervention is made with the following commands:
# drbdadm secondary resource
# drbdadm disconnect resource
# drbdadm -- --discard-my-data connect resource
On the other node (the split brain survivor), if its connection state is also StandAlone, you would enter:
# drbdadm connect resource
You may omit this step if the node is already in the WFConnection state; it will then reconnect automatically.
If all else fails and the machines are still in a split-brain condition then on the secondary (backup) machine issue:
drbdadm invalidate resource
The Recital Oracle Gateway requires the Oracle libclntsh.so shared library. If this file is unknown to ld.so.conf, add it using the ldconfig command.
Occasionally as a Linux administrator you will be in the situation where working on a remote server and you are left with no option but to force a reboot the system. This may be for a number of reasons, but where I have found it most frequent is when working on Linux clusters in a remote location.
When the "reboot" or "shutdown" commands are executed daemons are gracefully stopped and storage volumes unmounted.
This is usually accomplished via scripts in the /etc/init.d directory which will wait for each daemon to shut down gracefully before proceeding on to the next one. This is where a situation can develop where your Linux server fails to shutdown cleanly leaving you unable to administer the system until it is inspected locally. This is obviously not ideal so the answer is to force a reboot on the system where you can guarantee that the system will power cycle and come back up. The method will not unmount file systems nor sync delayed disk writes, so use this at your own discretion.
To force the kernel to reboot the system we will be making use of the magic SysRq key.
The magic_SysRq_key provides a means to send low level instructions directly to the kernel via the /proc virtual file system.
To enable the use of the magic SysRq option type the following at the command prompt:
echo 1 > /proc/sys/kernel/sysrq
Then to reboot the machine simply enter the following:
echo b > /proc/sysrq-trigger
Voilà! Your system will instantly reboot.
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./configure CFLAGS='-arch x86_64' APXSLDFLAGS='-arch x86_64' --with-apxs=/usr/sbin/apxsThen you must pass the these additional flags to the apxs command in order to generate a Universal Binary shared module.
-Wl,-dynamic -Wl,'-arch ppc' -Wl,'-arch ppc64' -Wl,'-arch i386' -Wl,'-arch x86_64' -Wc,-dynamic -Wc,'-arch ppc' -Wc,'-arch ppc64' -Wc,'-arch i386' -Wc,'-arch x86_64'If you then do a file command on the shared module it should return;
$ file mod_recital.so mod_recital2.2.so: Mach-O universal binary with 4 architectures mod_recital2.2.so (for architecture ppc7400): Mach-O bundle ppc mod_recital2.2.so (for architecture ppc64): Mach-O 64-bit bundle ppc64 mod_recital2.2.so (for architecture i386): Mach-O bundle i386 mod_recital2.2.so (for architecture x86_64): Mach-O 64-bit bundle x86_64The apache module files are stored in the /usr/libexec/apache2/ directory on a default apache install on the Mac and the configuration file is /private/etc/apache2/httpd.conf