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Wednesday, August 05, 2009

SSDs vs HDDs : WHO is GOOD?

1. Off late few notebook manufacturer's have been seen promoting their product for being the first to introduce SSDs. Now at the first glance they really seem to be promising since they offer less energy consumption, less weight, no mobile parts and also offer better speed in some ways than regular hard disk drives. But the question is whether they are strong enough to deliver the performance through out their life span. This puts a question mark????????????

2. If you have just bought a shiny new SSD, it isn’t likely to continue performing at blazing speeds after some usage. An empty drive will always perform better than one written to. The good news is that after an initial dip in performance, SSDs tend to level off. Even if they do drop in performance over time -- undercutting a manufacturer’s claims -- consumer flash drives are still vastly faster than traditional hard drives, because they can perform two to five times the input/output operations per second of a hard drive.

Why does performance drop?

3. Unlike a hard disk drive, any write operation to an SSD requires not one step, but two: an erase followed by the write. When an SSD is new, the NAND flash memory inside it has been pre-erased. But, as data is written to the drive, data management algorithms in the controller begin to move that data around the flash memory in an operation known as wear leveling. These algorithms are used to more evenly distribute data across flash memory so that no one portion wears out faster than another, which prolongs the life of whole drive. Even though wear-leveling is meant to prolong the life of the drive, it can eventually lead to performance issues. SSD performance and endurance are related.

4. Generally, the poorer the performance of a drive, the shorter the lifespan. That’s because the management overhead of an SSD is related to how many writes and erases take place. The more write/erase cycles there are, the shorter the drive’s lifespan. Consumer-grade Multi-Level Cell (MLC) memory can sustain from 2,000 to 10,000 write cycles. Enterprise-class Single- Level Cell (SLC) memory can last through 10 times the number of write cycles of an MLC-based drive.

What Matters ?

5. ALGORITHM : A read-modify-write algorithm in an SSD controller will take a block about to be written to, retrieve any data already in it, mark the block for deletion, redistribute the old data, then lay down the new data in the old block.

6. Some manufacturers use algorithms that combine writes to more efficiently use NAND flash memory space; others use cache to store writes in order to lay them down more efficiently.

7. BUGS : Bugs Can Cause Slow-Downs, Too Intel’s X25-M SSD had a firmware bug that led to major fragmentation problems that dropped throughput dramatically . But what’s clear is SSDs need more development to address these long term performance issues.

8. Thanks PC WORLD!!!


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