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<P><SPAN style="FONT-SIZE: 10pt">All,</SPAN></P>
<P><SPAN style="FONT-SIZE: 10pt"></SPAN> </P>
<P><SPAN style="FONT-SIZE: 10pt">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></P>
<P><SPAN style="FONT-SIZE: 10pt"></SPAN> </P>
<P><SPAN style="FONT-SIZE: 10pt">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></P>
<P><SPAN style="FONT-SIZE: 10pt"></SPAN> </P>
<P><SPAN style="FONT-SIZE: 10pt">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></P>
<P><SPAN style="FONT-SIZE: 10pt"></SPAN> </P>
<P><SPAN style="FONT-SIZE: 10pt">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></P>
<P><SPAN style="FONT-SIZE: 10pt"></SPAN> </P>
<P><SPAN style="FONT-SIZE: 10pt">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></P>
<P><SPAN style="FONT-SIZE: 10pt"></SPAN> </P>
<P><SPAN style="FONT-SIZE: 10pt">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></P>
<P><SPAN style="FONT-SIZE: 10pt"></SPAN> </P>
<P><SPAN style="FONT-SIZE: 10pt">Does anybody have any idea on how to optimally calculate the MAXIMUM UNMAP LAB COUNT value for NVMe.</SPAN></P>
<P><SPAN style="FONT-SIZE: 10pt"></SPAN> </P>
<P><SPAN style="FONT-SIZE: 10pt">Thanks,<BR>Suman</SPAN></P>
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