01 دى 1393, 08:04 ب.ظ
سلام
بچه ها من قسمت اول و دوم رو فهمیدم (تقریبا) اما پاراگراف سوم که میگه در SSD ها جدید دارن چی کار میکنن
هیچی نفهمیدم
یعنی مهم ترین قسمت مطلب همین قسمت هست که اوردنش
امکان داره کمک کنید؟ ممنون میشم
The smallest unit of NAND-based flash storage that can be
read or programmed (written) is a page (typically 4 KB in
size). All bits in a blank page are set to 1s, and writing
data to the page involves setting some of the bits within
it to 0s. Individual bits within a page cannot be reset to
1s; rewriting the page to a different bit pattern requires
an intermediate erase operation that resets all bits back to
1. These erasures are performed over large blocks (e.g.,
of 128 KB) spanning multiple pages. Blocks wear out as
they are erased, exhibiting increasing BERs that become
unmanageably high once the erasure limit is breached.
As a result of these fundamental constraints on write
operations, early flash-based devices that performed in-place
page modification suffered from very poor random write
latencies; writing to a randomly selected 4 KB page required
the entire 128 KB erase block to be erased and rewritten. In
addition, imbalanced loads that updated some pages much
more frequently than others could result in uneven wear
across the device.
To circumvent these problems, modern SSDs implement
a log-based block store, exposing a logical address space
that is decoupled from the physical address space on the
raw flash. The SSD maintains a mapping between logical
and physical locations at the granularity of an erase block.
A write to a random 4 KB page involves reading the surrounding
erasure block and writing it to an empty, previously
erased block, with no expensive erase operations in
the critical path. In addition, the mapping of logical to physical
blocks is driven by wear-leveling algorithms that aim
for even wear-out across the device. SSDs typically include
more raw flash than advertised in order to continue logging
updates even when the entire logical address space has been
occupied; for example, an 80 GB SSD could include an extra
10 GB of flash.
بچه ها من قسمت اول و دوم رو فهمیدم (تقریبا) اما پاراگراف سوم که میگه در SSD ها جدید دارن چی کار میکنن
هیچی نفهمیدم
یعنی مهم ترین قسمت مطلب همین قسمت هست که اوردنش
امکان داره کمک کنید؟ ممنون میشم
The smallest unit of NAND-based flash storage that can be
read or programmed (written) is a page (typically 4 KB in
size). All bits in a blank page are set to 1s, and writing
data to the page involves setting some of the bits within
it to 0s. Individual bits within a page cannot be reset to
1s; rewriting the page to a different bit pattern requires
an intermediate erase operation that resets all bits back to
1. These erasures are performed over large blocks (e.g.,
of 128 KB) spanning multiple pages. Blocks wear out as
they are erased, exhibiting increasing BERs that become
unmanageably high once the erasure limit is breached.
As a result of these fundamental constraints on write
operations, early flash-based devices that performed in-place
page modification suffered from very poor random write
latencies; writing to a randomly selected 4 KB page required
the entire 128 KB erase block to be erased and rewritten. In
addition, imbalanced loads that updated some pages much
more frequently than others could result in uneven wear
across the device.
To circumvent these problems, modern SSDs implement
a log-based block store, exposing a logical address space
that is decoupled from the physical address space on the
raw flash. The SSD maintains a mapping between logical
and physical locations at the granularity of an erase block.
A write to a random 4 KB page involves reading the surrounding
erasure block and writing it to an empty, previously
erased block, with no expensive erase operations in
the critical path. In addition, the mapping of logical to physical
blocks is driven by wear-leveling algorithms that aim
for even wear-out across the device. SSDs typically include
more raw flash than advertised in order to continue logging
updates even when the entire logical address space has been
occupied; for example, an 80 GB SSD could include an extra
10 GB of flash.