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fre 2013-09-06 klockan 09:46 +0200 skrev NOC:
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On 09/06/2013 08:11 AM, Karli Sjöberg wrote:
<font color="#737373">> What about swap? Don´t they have any swap file, or partition at all? </font>
<font color="#737373">> Swap-file over NFS must suck quite badly, no? We have bought </font>
<font color="#737373">> semi-cheap SSD's for our Hosts to use as swap to get more out of them </font>
<font color="#737373">> from memory overprovisioning.</font>
I don't quite see the point, unless you have mirrored ssd's. Data
corruption on ssd's is more frequent than on spinning disks and
disastrous when it happens in a swapped out page...
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Yes they absolutely need to be mirrored. I disagree though that modern SSD's are more failure-prone than spinning disks. I would rather say that they about as failure-prone as any other disk:<br>
<a href="http://www.tomshardware.com/reviews/ssd-reliability-failure-rate,2923-9.html">http://www.tomshardware.com/reviews/ssd-reliability-failure-rate,2923-9.html</a><br>
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And if you know which one's to buy, and which ones to watch out for, they may even last you longer:<br>
<a href="http://www.hardware-revolution.com/best-ssd-best-hdd-for-your-money-may-2013/">http://www.hardware-revolution.com/best-ssd-best-hdd-for-your-money-may-2013/</a><br>
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(And why not add
more RAM?)
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Well, for us, it´s mainly since we are extremely budget-constraint, using old, worn out servers that can´t handle putting in that much RAM. Also older servers require older RAM, which in turn are harder- and more expensive- to come by.<br>
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But why use swap at all? I'm assuming you dimension a node to its
intended use, so I guess lots of memory and CPU cores (in our case
anyway) and you can allocate the available memory to the VMs until it's
finished. I don't see much need for swap there.
Perhaps my view is different than usual, I see swap as the gravelly
escape roads on steep hills for trucks/cars who have failing breaks. It
just reduces the damage in case of unexpected failures.
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Is there a down-side to reduce damage in case of unexpected failures?:)<br>
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Swap isn't
something to use on a regular basis as cheep memory, as RAM is not that
expensive anymore and magnitudes faster.
/Simon
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Med Vänliga Hälsningar<br>
-------------------------------------------------------------------------------<br>
Karli Sjöberg<br>
Swedish University of Agricultural Sciences<br>
Box 7079 (Visiting Address Kronåsvägen 8)<br>
S-750 07 Uppsala, Sweden<br>
Phone: +46-(0)18-67 15 66<br>
<a href="mailto:karli.sjoberg@adm.slu.se">karli.sjoberg@slu.se</a> </td>
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