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Just to clarify this is SS compression, so </div>
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mmchattr --compression yes <filename></div>
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or an ILM equivalent</div>
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So not a regular modification.</div>
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Bob</div>
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<strong><span style="font-family:Arial,sans-serif,serif,EmojiFont; color:rgb(0,111,201); font-size:10pt">Bob Cregan</span></strong><span style="font-family:Arial,sans-serif,serif,EmojiFont; color:black; font-size:10pt"><br>
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<span style="font-size:10pt"></span><span style="font-family:Arial,sans-serif,serif,EmojiFont; color:black; font-size:10pt">Information & Communication Technologies</span><span style="font-family:Calibri,sans-serif,serif,EmojiFont; color:black"></span></p>
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<span style="font-size:10pt"></span><span style="font-family:Arial,sans-serif,serif,EmojiFont; color:black"><span style="font-size:10pt">Imperial College London, </span><br>
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<span style="font-size:10pt">E: b.cregan@imperial.ac.uk</span><br>
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<span style="font-size:10pt"></span><span style="font-family:Arial,sans-serif,serif,EmojiFont; color:black"><span style="font-size:10pt">W: </span><a href="http://www.imperial.ac.uk/ict/rcs" target="_blank" rel="noopener noreferrer" id="LPNoLP"><span style="font-size:10pt">www.imperial.ac.uk/</span><span style="font-size:10pt">ict</span><span style="font-size:10pt">/</span><span style="font-size:10pt">rcs</span></a></span><span style="font-family:Calibri,sans-serif,serif,EmojiFont; color:black"></span></p>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> Cregan, Bob<br>
<b>Sent:</b> 28 November 2019 09:43<br>
<b>To:</b> gpfsug main discussion list <gpfsug-discuss@spectrumscale.org><br>
<b>Subject:</b> Compression question</font>
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Hi All,</div>
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Can someone answer the following question on compression in a snapshot context? We have tried various experiments and they are inconclusive - too tedious to go into the detail.</div>
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What happens to the snapshot when a file is compressed in SS? The logic as I see it is </div>
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####### In a non compressed situation ###############</div>
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1) create a file,</div>
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2) create a snapshot.</div>
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3) modify a file in a normal way - the blocks on disk are changed and the old blocks are then written to the snap. </div>
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<p style="margin-top:0px; margin-bottom:0px">######In a compressed situation ############</p>
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<div style="margin:0px; font-family:Calibri,Arial,Helvetica,sans-serif">1) create a file,</div>
<div style="margin:0px; font-family:Calibri,Arial,Helvetica,sans-serif">2) create a snapshot.</div>
<div style="margin:0px; font-family:Calibri,Arial,Helvetica,sans-serif">3) Compress the file. Now IBM says the blocks are rewritten when the file is compressed. So do the old uncompressed blocks go into the snap? If so we now have 2 copies of the file and unless
the compression > 50% we have used more space until the snap is deleted.</div>
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<div style="margin:0px; font-family:Calibri,Arial,Helvetica,sans-serif">You get the space back in the end, but if you are in a tight situation then potentially compression might not work for you in the short term.</div>
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Thanks</div>
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Bob</div>
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<strong><span style="font-family:Arial,sans-serif,serif,EmojiFont; color:rgb(0,111,201); font-size:10pt">Bob Cregan</span></strong><span style="font-family:Arial,sans-serif,serif,EmojiFont; color:black; font-size:10pt"><br>
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<span style="font-size:10pt"></span><span style="font-family:Arial,sans-serif,serif,EmojiFont; color:black"><span style="font-size:10pt">Imperial College London, </span><br>
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