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Poll data comes in on the idea of virtualization

In a recent poll of nearly 2,000 DailyTech readers, worries about performance seemed to be the biggest potential objection to broader adoption of virtualization technology. Of the 1,998 respondents, 37 percent said they agreed with the statement that “virtualizing slows everything down.” Smaller numbers cited lack of redundancy (20 percent), complexity (12 percent), and cost (9 percent).

More than a fifth of the survey respondents – 439 readers, or 22 percent of the survey group – felt that there were no major drawbacks to virtualization technology, voicing their support for the statement, “Virtualization just rocks. Enough said.”

Several readers were vocal in their disagreement with the perception that virtualization can trigger performance issues. “Having worked with virtualization, I can say that performance should be `almost’ a non-issue with virtualization nowadays,” reader solgae1784 wrote in a comment posted to the DailyTech poll webpage.

“I say `almost’ because there are a few applications that (are) not suitable for virtualization,” solgae1784 added, noting that in such cases “you will see `near native’ performance due to overhead - even if the overhead is supposedly very small.”

DailyTech reader Mjello warned that running SQL on a virtualized server can be problematic. “If you have any sort of SQL on (the server), I’d urge you to not trust VM. If the server actually fails completely, hot migration (won’t) work,” Mjello wrote. “VM failover only works fully as long as the machine has something to migrate from. Otherwise it’s like pulling the plug on a normal server and then booting it again. Not a wise thing to do with a SQL under load.”

Lack of redundancy is a nonissue with virtualization, according to reader PorreKaj. “Virtualization can be expanded over several machines. For example, we have a little blade center with four blades running about 12 servers,” PorreKaj wrote. “If one blade blows up, WMware will just automatically assign the virtual servers to the other blades instantly - without interrupting the user.”

While DailyTech reader solgae1784 was generally bullish on virtualization, he did offer the advice that users should think carefully before choosing which CPU to place inside their virtualized machines. “Be warned that newer CPUs are much better for virtualization than the older CPUs,”  according to solgae1784. “The bottom line is, if you're going for virtualization, you may need to buy new servers. Make sure you do your homework to see if the initial investment will pay off in the long run. Then again, your servers may be due for a hardware refresh anyways.”



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RE: Ah, virtualization...
By Lord 666 on 8/26/2009 4:23:19 PM , Rating: 2
Thank you for the math on the I/O as thats always the trickiest part. However, what tools are the best in calculating the I/O prior to a P2V conversion?


RE: Ah, virtualization...
By amanojaku on 8/26/2009 7:57:03 PM , Rating: 2
In Windows open Perfmon and add the following counters:

Performance object: LogicalDisk (that's C:, D:, etc...)
Counters: Disk Reads/sec (Read IOPS), Disk Writes/sec (write IOPS), Disk Transfers/sec (Total IOPS)

Then you just need to know the IOPS of your disks (the vendor rarely likes to tell) and do the math. Something to consider is that RAID 5 and 6 sometimes require more drives and offer less performance than certain RAID 1+0 or 0+1 configurations.

To properly size a LUN determine the IOPS, then add some room for growth based on the current rate of change, then divide the IOPS needed by the IOPS of the drive, then see which drive capacity fits your needs based on the number of spindles.

In the example where I mentioned 6,000 IOPS you end up with 45 drives (43 + 1 parity + 1 spare.) 2.5TB/43 = 60GB. Someone building a RAID 5 with 10 300GB drives is going to wish he or she built a RAID 5 with 45 76GB drives, instead. Actually, not, because a RAID 5 with that many drives is a bad idea (higher potential for disk failure.) You would go RAID 1+0 or RAID 5+0 instead, and make a volume that tops out at 2,000 IOPS. With 15 drives you can get 1-2TB of high performance, protected storage for about 8 VMs with 100-200GB of space each. That's the general idea, anyway.


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