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6.3
SSD Lifetime Management
6.3.1
Total Bytes Written (TBW)
TBW (Terabytes Written) is a measurement of the SSDs' expected lifespan, which represents the amount of data
written to the device. To calculate the TBW of a SSD, the following equation is applied:
TBW = [(NAND Endurance) x (SSD Capacity)] / WAF
NAND Endurance: NAND endurance refers to the P/E (Program/Erase) cycle of a NAND flash. SSD Capacity: The SSD
capacity is the specific capacity in total of a SSD.
WAF: Write Amplification Factor (WAF) is a numerical value representing the ratio between the amount of data that a
SSD controller needs to write and the amount of data that the host's flash controller writes. A better WAF, which is near
1, guarantees better endurance and lower frequency of data written to flash memory.
TBW in this document is based on JEDEC 219 workload.
6.3.2
Media Wear Indicator
Actual life indicator reported by SMART Attribute byte index [5], Percentage Used, recommends User to replace drive
when reaching to 100%.
6.3.3
Read Only Mode (End of Life)
When drive is aged by cumulated program/erase cycles, media worn- out may cause increasing numbers of later bad
block. When the number of available spare is less the threshold(5%, SMART attribute log ID 02h Byte4), the drive will
notify Host through AER event and Critical Warning to enter Read Only Mode to prevent further data corruption. User
should start to replace the drive with another one immediately.
Seagate BarraCuda 510 SSD Product Manual, Rev A
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