Tag Archives: performance - Page 2

CX or VNX Mirrorview with Snapview active on the remote side

Posted by on January 21, 2014 No comments

If you have a primary LUN which is replicated using MirrorView/S and you decide to run SnapView snapshots on the remote side, consider that writes to the secondary LUN may have to wait for the COFW activity to complete before an acknowledgement is sent back to the primary array.

So if you’re performing tests on the remote site by using SnapView snapshots, you may want to consider suspending the MirrorView session(s) first in order to guarantee performance on the production site.

A good scenario would be to create clones from the temporary fractured mirrors and as soon as the clones are fully in sync, split the clone from its primary – being the MirrorView secondary – and start the resync in MirrorView.

MirrorView has to wait for SnapViewAfter the write from the primary array (1) a COFW (Copy On First Write) (2) must take place if the write (1) overwrites a block that hasn’t been written to yet in order to maintain the point in time of the snapshot. After the COFW (2) is complete the acknowledgement (ACK) (3) can be sent back to the primary array.

So even if the snapshot isn’t used by a host, there’s already an increased activity on the remote array.

If the snapshot is in use by a host that writes to the snapshot, an unchanged block on the secondary LUN need to be copied to the RLP (Reserved LUN Pool) first before the overwrite can take place. This will also slow down any ACKs that need to be sent back to the primary array.

Conclusion

Be very careful when starting SnapView sessions on a secondary LUN and even more careful when using the secondary LUNs since it can have a severe impact on the response times of the primary LUN.

The importance of keeping fibers clean

Posted by on March 12, 2013 1 comment

Fiber patch cables seem to be very forgiving, when light shines through everything is great and everybody’s happy, right? Wrong!!!
You shouldn’t underestimate the importance of keeping the ends of patch cables and the SFPs clean, since the actual diameter of a fiber is either 9 or 50 (or even 62.5) mu (micron).

fiber

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Performance Calculations on Clariion/VNX

Posted by on August 14, 2012 No comments

Although the actual story I want to point out to you is on the EMC Community Network website (also called ECN), I would like to invite you to join the discussion there:

https://community.emc.com/thread/148025?tstart=0

 

If you’d like to discuss anything here, you’re welcome to do so.

 

Let’s join the discussion!

Accelerating your storage array by using SSD technology

Posted by on July 8, 2011 6 comments

It’s out there since quite a few years already. It started becoming available to the general public about 12 years ago or so and was commonly seen in digital cameras: FLASH storage! At first the devices couldn’t store more than just a few MB and prices were high, but over time the size went up and prices went down and the first SSD drives (should we say “drives”?) were born. Still expensive but they were very usable in the computer industry. Mainly heavily used databases could be accelerated by using SSD because there was no rotational latency and avg access latency was in the sub mili second range instead of multiple mili seconds! The common problem in the last few years was mainly durability, but currently the SSD technology is just as reliable as the old rotating disks.

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