IBM has been secretly working on a technology that is changing the way administrators will deploy their VMware environments. SAN Volume Controller (SVC) Split Cluster solution allows live application mobility across data centers based on VMware Metro vMotion. This solution can now alleviate unplanned outages as well as provide additional flexibility.
SVC can now support a split cluster configuration where nodes can be separated by a distance up to 300 KM. This type of configuration does require clustering software at the application and server layer in order to failover to a server at the corresponding site in order to continue business and resume access to the disks. SVC will keep both copies of the storage in sync and mirror the cache between both nodes so the loss of one location does not disrupt data access at the other site.
The next big advantage SVC has is a small quorum disk that can allievate any split-brain issues. Split-brain problems occur when nodes are no longer abale to communicate with each other and they start allowing writes to their own data. SVC creates a tie break from a third site in order to ensure the survival of at least one location.
The SVC Split Cluster configuration uses a term called failure domain. This allows the SVC cluster to know which components are in a certain boundary where any failure may occur (ie power, fire, flood). The entire SVC Split Cluster must comprise of three such boundaries, two for the storage controllers containing the customer data and a third for the active quorum disk.
Using VMware’s VMFS file system, the SVC can supply access to all of the vSphere hosts in both locations. During vMotion, the virtual machine can switch to a new physical host while keeping the network identity. By using the Metro vMotion to migrate VMs, customers can now plan for disaster avoidance, load balancing as well as data center optimization of power and cooling.
This solution is also for customers looking to add high availability with in their single datacenter. Imagine two servers in different parts of the data center. They could be on different power feeds and different SAN fabrics. You can now provide continuous availability to these servers with out having an administrator called in the middle of the night.
For more information about SVC Split Cluster and even step by step instructions on how to setup the SVC, VMware and Layer2 network check out this Redbook.
Great article explaining site recovery adapters with VMware SRM. Thanks Tony.
This IBM® Redpaper® publication provides a basic introduction to the IBM System Storage® N series, virtualization using the Virtual Storage Console (VSC) 2.0 in VMware vSphere 4.x environments. It explains how to use the Virtual Storage Console with VMware vSphere 4 environments and the benefits of doing so. Examples are given on how to install and set up VSC.The Virtual Storage Console, which is an significant N series software product that works with VMware.
VSC provides local backup and recovery capability. You have the option to replicate backups to a remote storage system by using SnapMirror relationships. Backups can be performed on individual virtual machines or on datastores with the option of updating the SnapMirror relationship as part of the backup on a per job basis. Similarly, restores can be performed at a data-store level or individual virtual machine level.
IBM System Storage N series in conjunction with VMware vSphere 4 helps complete the virtualization hierarchy by providing both a server and storage virtualization solution. Although this configuration can further assist with other areas of virtualization, networks, and applications, these areas of virtualization are not covered in detail in this paper.This is a companion IBM® Redpaper® to “IBM System Storage N series with VMware vSphere 4.1”, SG24-7636.
My father is a retired teacher but loves to work with his hands. I can remember very early on in my up bringing, him teaching me that it is good to measure twice and cut once. Whether it was building a deck or just a bird house the point was it took more time to cut something wrong and then has to re-cut the board shorter or even wastes the old board and cut a whole new one.
When I was preparing for this article I remember having to learn that lesson the hard way and how much effort really is put into that second cut. The problem in the storage industry is the misaligned partitions from a move of a 512 byte sector to a new 4096 byte sector. This has to be one of the bigger performance issues with virtualized systems and new storage.
Disk drives in the past had a limit on the number of sectors to 512 bytes. This was ok when you had a 315 MB drive because the number of 512 byte blocks was not nearly as large as what is in a 3 TB drive of today’s’ systems. Newer versions of Windows and Linux will transfer the 4096 data block that match the native hard disk drive sector size. But during migrations even new systems can have an issue.
There is also something called 512 byte sector emulation which is where a 4k sector on the hard disk is remapped to 8 512 byte sectors. Each read and write would be done in eight 512 byte sectors.
When the older OS is created or migrated, it may or may not align the first block in the eight block group with the beginning of the 4k sector. This causes misalignment of a one block segment. As the reads and writes are laid down on the disks the misalignment of the logical sectors from the physical sectors mean the 8 512 byte blocks now occupy 2 4k sectors.
This now forces the disk to perform an additional read and/or write to two physical 4k sectors. It has been documented that sector misalignment can cause a reduction in write performance of at least 30% for a 7200 RPM hard drive.
This issue is only magnified when adding other file systems on top of this misalignment. When using a hyper visor like VMWare or Hyper-V, the virtual image can be misaligned and cause even further performance degradation.
There are hundreds of articles and blogs written on how to check for you disk alignment. A simple Google search of the words “disk sector alignment” and you will find this has been a very popular topic. Different applications will have different ways of checking and possibly realigning the sectors.
One application that can help you identify and fix these is a tool called the Pargon Alignment tool. This tool is easy to use and will automatically determine if a drive’s partitions are misaligned. If there is misalignment the utility then properly realigns the existing partitions including boot partitions to the 4k sector boundaries.
I came across this tool when looking for something to help N series customers who have misalignment issues in virtual systems. One of the biggest things I saw as an advantage was this tool can align partitions while the OS is running and does not require the snapshots to be removed. It also can align multiple VMDKs within a single virtual machine.
For more information on this tool and alignment check out the Paragon Software Group website.
In the end, your alignment will effect how much disk space you have, how much you can dedupe and the overall performance of your storage system. It pays to check this before you start having issues and if you are already seeing problems I hope this can help.
Now available is the IBM System Storage N series with VMware vSphere
Redbooks are a great way of learning a new technology or a reference for configuration. I have used them for years not just in storage but for X series servers and for software like TSM. The people that write the books spend a great deal of time putting them together and I believe most of them are written by volunteers.
This is the third edition of this Redbook and if you have read this before here are some of the changes:
-Latest N series model and feature information.
-Updated the IBM Redbook to reflect VMware vSphere 4.1 environments
-Information for Virtual Storage Console 2.x has been added
This book on N series and VMware goes through the introduction of both the N series systems and VMware vSphere. There are sections on installing the systems, deploying the LUNs and recovery. After going through this Redbook, you will have a better understanding of a complete and protected VMware system. If you need help with how to size your hardware there is a section for you. If you are looking to test how to run VMs over NFS, its in there too!
One of the biggest issues with virtual systems is making sure you have proper alignment between the system block and the storage array. This will negatively impact the system by a factor of 2 in most random reads/writes as two blocks will be required for one request. To avoid this costly mistake or to correct VMs you have already setup a section in the book called Partition alignment walks you through the entire process of correctly setting the alignment or fixing the older systems correctly.
Another area that I will point out is the use of deduplication, compression and cloning to drive the efficiency of the storage higher. These software features allow customers to store more systems on the storage array than if they used traditional hard drives. Also there is how to use snapshots for cloning, mirrors for Site Recovery Manager and long term storage aka Snapvaults. At the end of the book are some examples of scripts one might use for snapshots in hot backup modes.
Whether you are a seasoned veteran or newbie to the VMware scene, there is a great guide that will help you from start to finish setting up your vSphere environment. The information is there, use the search feature or sit down on a Friday with a high-lighter, which ever fits your style and learn a little about using a N series system with VMware.
Here is the link to this Rebook: