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  • PaaS |
    Monday, May 16, 2016

Database as a Virtual Image

The question that we are going to dive into this week is what does it really mean to be platform as a service vs infrastructure as a service. Why not go to Amazon and spin up an EC2 instance or search for an Oracle provided AMI on Amazon or Virtual Image on Azure? What benefit do I get from PaaS? To answer that we need to look at the key differences. Let's look at the two options when you provision a database in the Oracle DBaaS. When you provision a database you have the option of service levels; Database Cloud Service and Database Cloud Service - Virtual Image. We looked at the provisioning of the cloud service. It provisions a database, creates the network rules, and spins up an instance for us. What happens when we select Virtual Image?


The release and version screens are the same. We selected 12c for the release and High Performance for the version. Note that the questions are much simpler. We are not asked about how much storage. We are not asked for an SID or sys password. We are not asked about backup options. We are not given the option of DataGuard, RAC, or GoldenGate. We are only asked to name the instance, pick a compute shape, and provide an ssh public key.

This seems much simpler and better. Unfortunately, this isn't true. What happens from here is that a Linux 6.6 instance is created and a tarball is dropped into a staging area. The database is not provisioned. The file system is not prepared. The network ports are not configured and enabled. True, the virtual instance creation only takes a few minutes but all we are doing is provisioning a Linux instance and copying a tarball into a directory. Details on the installation process can be found at Database Cloud Installation - Virtual Image Documentation.

If you look at the detailed information about a system that is being created with a virtual image and a system that is being created as a service there are vast differences.


The first key difference is the amount of information displayed. Both instances have the same edition, Enterprise Edition - High Performance. Both will display this difference in the database as well as in the banner if asked what version the database is. The Service Level is different with the virtual image displayed as part of the service level. This effects the billing. The virtual image is a lower cost because less is done for you.












Product (per OCPU)General Purpose High-Memory
Per MonthPer HourPer MonthPer Hour
Standard Edition Service$600$1.008$700$1.176
Enterprise Edition Service$3,000$5.040$3,100$5.208
High Performance Service$4,000$6.720$4,100$6.888
Extreme Performance Service$5,000$8.401$5,100$8.569












Virtual Image Product (per OCPU)General Purpose High-Memory
Per MonthPer HourPer MonthPer Hour
Standard Edition Service$400$0.672$500$0.840
Enterprise Edition Service$1,500$2.520$1,600$2.688
High Performance Service$2,000$3.360$2,100$3.528
Extreme Performance Service$3,000$5.040$3,100$5.208

The only other information that we get from the management screen is that the instance comsumes 30 GB rather than 100 GB that the database service instance consumes. Note that the database service instance also has the container name and a connection string for connecting to the database. Both will eventually show an ip address and we should look into the operating system to see the differences. The menu to the right of the instance is also different. If we look at the virtual machine instance we only see ssh access, access rules, and deletion of the instance as options.


The ssh access allows us to upload the public key or look at the existing public key that is used to access the instance. The access rules takes us to a new screen that shows the security rules that have been defined for this instance, which is only ssh and nothing else.

If we look at a database as a service instance, the menu is different and allows us to look at things like the DBaaS Monitor, APEX, Enterprise Manager monitor, as well as the ssh and access rules.

Note that the database as a service instance has a lot more security rules defined with most of them being disabled. We can open up ports 80, 443, 4848, 1158, 5500, and 1521. We don't have to define these rules, just enable them if we are accessing them from a whitelist, ip address range, or public internet.

Once we connect to both instances we can see that both are running

Linux hostname 3.8.13-68.2.2.2.el6uek.x86_64 #2 SMP Fri Jun 19 16:29:40 PDT 2015  x86_64 x86_64 x86_64 GNU/Linux

We can see that the file system is different with the /u01, /u02, /u03, and /u04 partitions not mounted in the screen shots below.


If we look at the installation instructions we see that we have to create the /u01, /u02, /u03, and /u04 disks by hand. These are not created for us. We also need to create a logical volume as well as creating the storage services. Step one is to scale up the service by adding a disk. We need to grow the existing file system by first attaching a logical volume then laying out/expanding the logical volume that we have. Note that we can exactly mirror our on-premise system at this point. If we put everything into a 1 TB /u01 partition and blend the log files and data files into one disk (not really recommended) we can do this.

To add the /u01 disk we need to scale up the service and add storage. Note that we only can add a raw disk and can not grow the data volume as we can with the database service.



Note that this scale up does require a reboot of the service. We have the option of adding one logical unit or a full 1 TB disk then partitioning it or we can add the different volumes into different disks. The drawback of doing this is that the way that attached storage is charged is $50/TB/month so adding four disks that consume 20 GB each will consume $200/month because we are allocated the full 1 TB even though we just allocate 20 GB on each disk. We do not subdivide the disk when it is attached and are charged on a per TB basis and not a per GB basis. To save money it is recommended to allocate a full TB rather than a smaller amount. To improve performance and reliability it is recommended to allocate multiple disks and stripe data across multiple spindles and logical units. This can be done at the logical volume management part of disk management detailed in the documentation in provisioning the virtual image instance.

We can look at the logical volume configuration with the lvm pvdisplay, lvm vgdisplay, and lvm lvdisplay. This allows us to look at the physical volume mapping to map physical volumes to logical unit numbers, look at logical volumes for mirroring and stripping options, and volume group options which gets mapped to the data, reco, and fra areas.





Once our instance has rebooted we note that we added /dev/xvdc which is 21.5 GB in size. After we format this disk it partitions down to a 20 GB disk as we asked. If we add a second disk we will get /dev/xvdd and can map these two new disks into a logical volume that we can map to /u01/and /u02. A nicer command to use to look at this is the lsblk command which does not require elevated root privileges to run.

Once we go through the mapping of the /u01, /u02, /u03, and /u04 disks (the documentation only goes into single disks with no mirroring to mount /u01 and /u02) we can expand the binary bits located in /scratch/db. There are two files in this directory, db12102_bits.tar.gz and db12102_se2bits.tar.gz. These are the enterprise edition and standard edition versions of the database.

We are not going to go through the full installation but look at some of the key differences between IaaS with a tarball (or EC2 with an AMI) and a DBaaS installation. The primary delta is that the database is fully configured and ready to run in about an hour with DBaaS. With IaaS we need to create and mount a file system, untar and install the database, configure network ports, define security rules, and write scripts to automatically start the database upon restarting the operating system. We loose the menu items in the management page to look at the DBaaS Monitor, Enterprise Manager monitor, and Application Express interface. We also loose the patching options that appear in the DBaaS management screen. We loose the automated backup and database instance and PDB creation as is done with the DBaaS.

In summary, the PaaS/DBaaS provisioning in not only a shortcut but removes manual steps in configuring the service as well as daily operations. We could have just as easily provisioned a compute service, attached storage, downloaded the tarball that we want to use from edelivery.oracle.com. The key reasons that we don't want to do this are first pricing and second patching. If we provision a virtual image of database as a service the operating system is ready to accept the tarball and we don't need to install the odbc drivers and other kernel modules. We also get to lease the database on an hourly or monthly basis rather than purchasing a perpetual license to run on our compute instance.

Up next, selecting a pre-configured AMI on Amazon and running it in AWS compared to a virtual image on the Oracle Public Cloud.

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