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Disparity between read/write speeds when performing SVMotion

Posted on 2014-08-05
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Last Modified: 2014-08-09
Last night I performed a SVMotion on a VM from a SSD to a 6 disk RAID10.  The read/write rates are shown in the attached graphic.  Any idea why my read rate would be 1/2 my write rate?  It seems to me that, at the very least, they should be equal?  How can a disk write faster than the data being read?
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Question by:sbumpas
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by:theruck
ID: 40241119
your raid controller uses battery write cache module which is essentially a RAM which has much higher transfer rates than any SSD chips. anyway you can see that these graphs show nothing real and that vmware (and also other vendors) are just giving you something you do not need.
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by:sbumpas
ID: 40241127
The write cache was my first thought, but you can see in the start in the xfer the speeds are much higher - presumably while the cache is in use.  Once cache is full, the speeds bottom out (a bit) but the writes are still 2x faster.  

What do you mean the graphs "show nothing real"?
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theruck earned 2000 total points
ID: 40241146
the graphs show something but as you stated you know you can not write faster than read. at least not for such a long time. so the graph is there just to be there for marketing purposes and it is nothing you can trust. at least not the way you understand its usage.
another thing could be that it shows the data incorrectly due to some explainable reasons. like sumarising the write of all the disk spindles in the destination raid etc.
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What do you mean the graphs "show nothing real"?

if you want a longer discussion, leave the question to run for longer, for the storage Experts!
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by:sbumpas
ID: 40241208
I would love to know more - do I need to repost since I accepted an answer?
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