Introducing the IBM BladeCenter
The IBM BladeCenter is a reflection of IBM technology sharing. But be careful, this architecture assumes that you as the customer will be the technology integrator. IBM technology sharing does not necessarily include the desire to make this product easy to setup and maintain. Our industry has adopted a certain level of complexity as we've moved towards a greater use of commodity (read that Intel) servers. IBM is a part of that overall trend.
Let me preface my subsequent remarks by disclosing that my views of the BladeCenter are heavily influenced by my long history of, and affiliation with, the IBM AS/400 and its successors.
First of all, the IBM BladeCenter is an architecture. Customers should not consider its purchase in the same manner they would if they were buying individual servers. With the IBM BladeCenter you are effectively investing in the chassis, and expending for the servers. In other words, the servers, like any other Intel based servers, will ultimately be a throwaway item over time, while the chassis will remain in place..
If you are considering a BladeCenter, please note that they only become cost effective when you have at least 5 physical blades to populate in the chassis. I won't bore you with the math, since that changes with pricing actions, but suffice it to say that if you need less than 5 servers, forget the BladeCenter.
Do you currently have a SAN? Do you understand how to manage a SAN? Why do I ask these questions? I ask them because the BladeCenter will drag the use of a SAN. With the exception of the BladeCenter S, the BladeCenter itself does not have storage. Of course, the individual Blades may contain one or two disk drives, but the the use of those drives varies by the operating system being deployed on that Blade. How this affects AS/400, iSeries, and System i customers I will explain momentarily.
I have spoken with System i customers who view the BladeCenter as an inexpensive alternative to the traditional System i that comes in either a rack or tower form factor. The reason at first appears simple, the cost of a Power6 blade is relatively inexpensive, at under $ 5,000. Unfortunately, there are numerous other considerations that should factor into your decision. One consideration is not so obvious, and that is from whom to purchase your Power6 Blade ( JS12 or JS22).
I know of a customer who had iSeries and pSeries and BladeCenters installed in their environment. The customer thought the new Power6 Blade would be an ideal way too host their iSeries applications going forward. To that end, they contacted their business partner and purchased a new JS22. This was hailed as a great decision since this customer had all the skills in-house to make this a deployment a success.
There was just one small problem. When they went to purchase the operating system from their business partner they found they could not. Their business partner was sanctioned by IBM to sell System p, AIX, Blades and IBM SANs, but they did not have the value add to sell IBM i (aka OS/400). They were never an iSeries business partner. That was not their heritage.
Eventually the problem was resolved, but it was messy. The bottom line is that IBM makes no distinction between business partners when it comes to the JS21 and JS22. So a business partner might inadvertently sell a Power6 Blade and not be able to sell the desired operating system.
In the above example the customer believed they had all of the skill sets to make the JS22 work with both the BladeCenter and IBM i. In my opinion, most iSeries customers do not possess those skills nor do most of IBM's business partners.
If one successfully downloads and installs all the various firmware and patches for the Advanced Management Module and the other I/O modules that were purchased, then they will be in a position to install the Power6 Blade (JS12, JS22, JS23 or JS43) and then install the operating system. I won't go into detail, but this initial process is tedious and must be done very, very carefully.
VIOS: Another operating system to worry about
At that point in time your are ready to focus on the install of the Power6 blade. However, there are some things you must first understand about the architecture of IBM i in a BladeCenter. For those that don't know, the System i on a Blade is a partitioned server, meaning that you will always have at least 2 LPARs on the Power6 Blade you install. One LPAR will house IBM i and the other will host VIOS.
VIOS is the Virtual IO Server, a subset of AIX. Stated another way, VIOS is essentially a limited use AIX LPAR dedicated to serve I/O devices to IBM i. It is VIOS that owns the I/O that IBM i needs to operate. In other words, IBM i cannot directly access the disk drives. VIOS see the disks via the I/O adapters, maps the drives for IBM i, and then presents them to IBM i as if they were native. VIOS also owns the tape drive(s) and the Ethernet adapter(s) and it presents those to IBM i too.
One implication of using VIOS is that you can forget IBM i based disk management. This is a shame since the gem of operating system, even from the days of OS/400, was it's disk management. That has now been compromised in the BladeCenter. Disk management is now the province of VIOS and the SAN that ultimately holds all objects. IBM i was very advanced in managing DASD, and in my opinion this new design is a step backwards. Whereas on a dedicated System i you can get direct access to your data, on the BladeCenter you must go through two constructs (VIOS and the SAN OS) to get to your objects. Is this more efficient? Are there more points of failure? I think so.
It should also be noted that even though the Power6 blades can have one or two disk drives, these on-board drives can only house the operating system (IBM I); they cannot be used to store your data. Data must always reside on external DASD.
Backup requires VIOS
Another major implication of VIOS is tape backup. Forget your current automated backup routine. When originally introduced in 2008, the way backup worked was that your objects were copied up to an optical image first and then to tape. They called it an optical image but actually the backing was to a disk image first. That means you needed at least as much free disk space as you had objects to back up.
Could you automate this process? Sure, if you understood the VIOS scripting language. There is an good publication about VIOS on IBM's web site. One could learn about the scripting language by reading that publication. Personally, I wondered why our colleagues in IBM Rochester did not provide such scripts so that customers could obtain some level of automation. Most of the customers I know still backup their data on a schedule.
In IBM Announcement letter 109-231 of April 28, 2009 support became available for direct backup to selected LTO-4 tape drives that are attached via VIOS. Native save/restore commands and BRMS can now be used with these drives. However, IBM calls this function virtual tape although IBM I already has a virtual tape function that was introduced in i5/OS V5R4.
In the same announcement IBM introduced the new JS23 and JS43 Power blades. These new blades are 4-core and 8-core implementations supporting up to 64Gbs and 128Gbs of memory, respectively. Omitted from this notice was any mention of their CPW ratings.
It is the CPW rating for the Power6 blades that is the most troubling aspect of this product. IBM has presented a very misleading statement of performance for this product. Let me explain. The JS12 has a 2-core 3.8GHz POWER6 processor. IBM quotes a CPW rating for this blade of 7,100.( http://www-03.ibm.com/systems/bladecenter/hardware/servers/js12/perfdata.html ). This ratingwas achieved under test with 90-drives assigned to IBM i, and with .2 processors assigned VIOS. How many System i customers would have 90-drives attached to IBM i on a Power blade? That equates to at minimum some 6.5 Terabytes if disk.
The IBM Power Systems Performance Capabilities Reference IBM i Operating System 6.1 is the published authority on performance matters. A careful reading of that text yields a very different expectation. ( http://www-03.ibm.com/systems/resources/systems_i_advantages_perfmgmt_pdf_pcrm.pdf ) If you look in Appendix C1 on page 333 you will note that IBM says that a 12 disk configuration associated JS12 would be equivalent to a 1,200 CPW server (or only 100 CPW per disk drive). I Think that it is safe to say that if you have less than 2 Terabytes of disk being used under IBM i, that your performance is more likely to be in the 1,200 CPW range (or 83% less than IBM is quoting on their web page).
In summary, given the issues with backup and overall performance I cannot see how the Power6 blade implementation can be viewed as a practical platform for most System i customers.
No comments:
Post a Comment