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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Currently, I’m unaware of optimal settings for NVMe devices in general. My take on this is that the value used should be vendor specific. Meaning that each vendor’s
NVMe drive will have a specific value to that vendor, regardless of a generic formula. Performing the same TRIM command may take longer on some devices than others. I believe this is why the value is defined in a very specific VPD Inquiry page.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Thanks,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Ray
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="margin:0in;margin-bottom:.0001pt"><b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> nvmewin-bounces@lists.openfabrics.org [mailto:nvmewin-bounces@lists.openfabrics.org]
<b>On Behalf Of </b>SUMAN PRAKASH B<br>
<b>Sent:</b> Friday, May 22, 2015 12:05 AM<br>
<b>To:</b> nvmewin@lists.openfabrics.org<br>
<b>Subject:</b> [nvmewin] regarding slower disk format time<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p><span style="font-size:10.0pt">All,</span><o:p></o:p></p>
<p> <o:p></o:p></p>
<p><span style="font-size:10.0pt">This is regarding the slower disk format time with the OFA driver compared to Inbox driver on Windows 8.1. Uma Parepalli(skhms) had raised the same concern in February.</span><o:p></o:p></p>
<p> <o:p></o:p></p>
<p><span style="font-size:10.0pt">In OFA driver, the maximum number of blocks that can be de-allocated, which driver assigns in the MAXIMUM UNMAP LBA COUNT field in Inquiry - Block Limits VPD page is set to 0xFFFF, which is the maximum number of logical blocks
for a read or write command. Hence during format, OFA driver gets SCSI UNMAP commands with UNMAP DATA LENGTH set to 0xFFFF at max, always.</span><o:p></o:p></p>
<p> <o:p></o:p></p>
<p><span style="font-size:10.0pt">The value in MAXIMUM UNMAP LBA COUNT field in Inquiry - Block Limits VPD page has to be set to a higher value based on the logical block size, so that driver will get lesser number of SCSI Unmap commands. We have observed during
quick format on a 400GB density disk, OFA driver gets ~6000 Unmap commands.</span><o:p></o:p></p>
<p> <o:p></o:p></p>
<p><span style="font-size:10.0pt">For ATA devices, following is the formula to calculate the MAXIMIMUM UNMAP LBA COUNT value:<br>
The BLOCK LIMITS VPD page MAXIMUM UNMAP LBA COUNT is calculated by multiplying the value of IDENTIFY DEVICE word 105 with 4194240 (65535 blocks per LBA range × 64 LBAranges per 512-byte block).</span><o:p></o:p></p>
<p> <o:p></o:p></p>
<p><span style="font-size:10.0pt">We did not find any standard way of calculating the MAXIMUM UNMAP LBA COUNT value for NVMe. The SCSI - NVMe translation spec mentions that this value should be > 0.</span><o:p></o:p></p>
<p> <o:p></o:p></p>
<p><span style="font-size:10.0pt">We can set the MAXIMUM UNMAP LBA COUNT value to the maximum possible length in logical blocks i.e, 0xFFFF_FFFF. With this, the format performance is as good as MS Inbox driver. But this may not work for bigger density disks
as there will be risk of causing a time out while processing a Unmap command for large values of logical blocks.</span><o:p></o:p></p>
<p> <o:p></o:p></p>
<p><span style="font-size:10.0pt">Does anybody have any idea on how to optimally calculate the MAXIMUM UNMAP LAB COUNT value for NVMe.</span><o:p></o:p></p>
<p> <o:p></o:p></p>
<p><span style="font-size:10.0pt">Thanks,<br>
Suman</span><o:p></o:p></p>
<p style="margin-bottom:12.0pt"><o:p> </o:p></p>
<p class="MsoNormal" style="margin:0in;margin-bottom:.0001pt"><img id="_x0000_i1025" src="http://ext.samsung.net/mailcheck/SeenTimeChecker?do=502122e85cbba61a0ce65e18eb501182daf257cfe78672b87d9badbdf7e30042d1afaaba7860cdcd9564217c646641ad61e16949eaa607501b20909a04efd4d2748cfe1d4e847419cf878f9a26ce15a0"><o:p></o:p></p>
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