<div class="socmaildefaultfont" dir="ltr" style="font-family:Arial, Helvetica, sans-serif;font-size:10.5pt" ><div dir="ltr" >Shaun,</div>
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<div dir="ltr" >have you had a look at the following section of the knowledge centre?</div>
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<div dir="ltr" ><a href="https://www.ibm.com/support/knowledgecenter/en/STXKQY_5.0.0/com.ibm.spectrum.scale.v5r00.doc/bl1adm_compression.htm#compression__sec_updates">https://www.ibm.com/support/knowledgecenter/en/STXKQY_5.0.0/com.ibm.spectrum.scale.v5r00.doc/bl1adm_compression.htm#compression__sec_updates</a></div>
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<div dir="ltr" >I think the answer to your question is going to depend on a number of factors:</div>
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<div dir="ltr" >1) number of blocks the file takes up - if its less than 10 then it is contained in a single compression group, if its more than 10 it will be dispersed over a number of compression groups, if it is less than 2 blocks it won't be compressed at all.</div>
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<div dir="ltr" >See : Limitations </div>
<div dir="ltr" >File compression processes each compression group within a file independently. A compression group consists of one to 10 consecutive data blocks within a file. If the file contains fewer than 10 data blocks, the whole file is one compression group. If the saving of space for a compression group is less than 10%, file compression does not compress it but skips to the next compression group.</div>
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<div dir="ltr" >2) in terms of deletion that is effectively a write update.. in which case the following would apply.</div>
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<div dir="ltr" ><span style="color: rgb(50, 50, 50); font-family: ibm-plex-sans, "Helvetica Neue", Arial, sans-serif; font-size: 16px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; background-color: rgb(255, 255, 255); text-decoration-style: initial; text-decoration-color: initial; display: inline !important; float: none;" >When a compressed file is updated by a write operation, the file system automatically decompresses the region of the file that contains the affected data and sets the<span> </span></span><samp class="ph systemoutput" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; font-size: 16px; font-family: ibm-plex-mono, Menlo, "DejaVu Sans Mono", "Bitstream Vera Sans Mono", Courier, monospace; word-break: break-word; color: rgb(50, 50, 50); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; background-color: rgb(255, 255, 255); text-decoration-style: initial; text-decoration-color: initial;" >illCompressed</samp><span style="color: rgb(50, 50, 50); font-family: ibm-plex-sans, "Helvetica Neue", Arial, sans-serif; font-size: 16px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; background-color: rgb(255, 255, 255); text-decoration-style: initial; text-decoration-color: initial; display: inline !important; float: none;" ><span> </span>flag. The file system then makes the update. To recompress the file, run the<span> </span></span><span class="keyword cmdname" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; font-size: 16px; text-indent: 0px; font-weight: 700; font-family: ibm-plex-mono, Menlo, "DejaVu Sans Mono", "Bitstream Vera Sans Mono", Courier, monospace; word-break: break-all; color: rgb(50, 50, 50); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; letter-spacing: normal; orphans: 2; text-align: start; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; background-color: rgb(255, 255, 255); text-decoration-style: initial; text-decoration-color: initial;" >mmrestripefile</span><span style="color: rgb(50, 50, 50); font-family: ibm-plex-sans, "Helvetica Neue", Arial, sans-serif; font-size: 16px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; background-color: rgb(255, 255, 255); text-decoration-style: initial; text-decoration-color: initial; display: inline !important; float: none;" ><span> </span>command with the<span> </span></span><span class="keyword parmname" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; font-size: 16px; text-indent: 0px; font-weight: 700; font-family: ibm-plex-mono, Menlo, "DejaVu Sans Mono", "Bitstream Vera Sans Mono", Courier, monospace; white-space: pre-line; color: rgb(50, 50, 50); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; letter-spacing: normal; orphans: 2; text-align: start; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; background-color: rgb(255, 255, 255); text-decoration-style: initial; text-decoration-color: initial;" >-z</span><span style="color: rgb(50, 50, 50); font-family: ibm-plex-sans, "Helvetica Neue", Arial, sans-serif; font-size: 16px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; background-color: rgb(255, 255, 255); text-decoration-style: initial; text-decoration-color: initial; display: inline !important; float: none;" ><span> </span>option, as in the following example:</span> </div>
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<div dir="ltr" >if the file is dispersed over multiple compression groups then the illcompressed flag will apply on the groups that have been updated, and the next time the compression policy is run they will be recompressed.</div>
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<div dir="ltr" >in terms of performance overhead -- the answer will always be -- it depends on your specific data environment.</div>
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<div dir="ltr" >Regards,</div>
<div dir="ltr" ><div class="socmaildefaultfont" dir="ltr" style="font-family:Arial;font-size:10.5pt" ><div class="socmaildefaultfont" dir="ltr" style="font-family:Arial;font-size:10.5pt" ><div class="socmaildefaultfont" dir="ltr" style="font-family:Arial;font-size:10.5pt" ><div dir="ltr" style="margin-top: 20px;" ><div style="font-size: 12pt; font-weight: bold; font-family: sans-serif; color: #7C7C5F;" >Andrew Beattie</div>
<div style="font-size: 10pt; font-weight: bold; font-family: sans-serif;" >Software Defined Storage - IT Specialist</div>
<div style="font-size: 8pt; font-family: sans-serif; margin-top: 10px;" ><div><span style="font-weight: bold; color: #336699;" >Phone: </span>614-2133-7927</div>
<div><span style="font-weight: bold; color: #336699;" >E-mail: </span><a href="mailto:abeattie@au1.ibm.com" style="color: #555">abeattie@au1.ibm.com</a></div></div></div></div></div></div></div>
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<blockquote data-history-content-modified="1" dir="ltr" style="border-left:solid #aaaaaa 2px; margin-left:5px; padding-left:5px; direction:ltr; margin-right:0px" >----- Original message -----<br>From: Shaun Anderson <SAnderson@convergeone.com><br>Sent by: gpfsug-discuss-bounces@spectrumscale.org<br>To: "gpfsug-discuss@spectrumscale.org" <gpfsug-discuss@spectrumscale.org><br>Cc:<br>Subject: [gpfsug-discuss] Compression details<br>Date: Thu, Jul 26, 2018 5:16 AM<br> <br><!--Notes ACF
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<p>I've had the question come up about how SS will handle file deletion as well as overhead required for compression using zl4.</p>
<p> </p>
<p>The two questions I'm looking for answers (or better yet, reference material documenting) to are:</p>
<p> </p>
<p>1)</p>
<p>- How is file deletion handled?</p>
<p> </p>
<p>Is the block containing the compressed file decompressed, the file deleted, and then recompressed? Or is metadata simply updated showing the file is to be deleted? Does Scale run an implicit 'mmchattr --compression no' command? </p>
<p> </p>
<p>2)</p>
<p>- Are there any guidelines on the overhead to plan for in a compressed environment (lz4)? I'm not seeing any kind of sizing guidance. This is potentially going to be for an exisitng ESS GL2 system.</p>
<p> </p>
<p>Any assistance or direction is appreciated.</p>
<p> </p>
<p>Regards,</p>
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