VSAN-Troubleshooting-Reference-Manual

Diagnostics and Troubleshooting Reference Manual – Virtual SAN
Flash Considerations in version 6.0
For Virtual SAN 6.0, the endurance class has been updated to use Terabytes Written
(TBW), over the vendor’s drive warranty. Previously the specification was full Drive
Writes Per Day (DWPD).
By quoting the specification in Terabytes Written (TBW), VMware allows vendors
the flexibility to use larger capacity drives with lower full Drive Writes Per Day
(DWPD) specifications.
For instance, a 200GB drive with 10 full DWPD is equivalent to a 400GB drive with 5
full DWPD from an endurance perspective. If VMware kept a specification of 10
DWPD, the 400 GB drive with 5 DWPD would be excluded from the Virtual SAN
certification.
By changing the specification to 2 TBW per day, both the 200GB drive and 400GB
drives are qualified - 2 TBW per day is the equivalent of 5 DWPD for the 400GB
drive and is the equivalent of 10 DWPD for the 200GB drive.
Of course, this is also a useful reference for the endurance of flash devices used on
the capacity layer, but these devices tend not to require the same level of endurance
as the flash devices used as the caching layer.
Class SSD Tier TBW (Per Day) TBW (5 years)
A All Flash Capacity 0.2 365
B Hybrid – Caching 1 1825
C All Flash – Caching (medium workloads) 2 3650
D All Flash – Caching (high workloads) 3 5475
All-Flash device considerations
VMware is supporting flash drives for capacity in the 6.0 versions of Virtual SAN.
Flash drives have shown themselves notoriously sensitive to firmware levels and
requiring updates. Once flash drives for capacity start to appear on the VCG, ensure
that you use the most recent versions of drivers and firmware.
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