learning about all flash arrays

I started learning about flash arrays as all flash array started occupying data center floors and trend is going to continue for next 5 to 10 years. Gartner predicts in a report that “By 2019, 20% of traditional high-end storage arrays will be replaced by dedicated solid-state arrays (SSA).”.let me start this flash series by explaining new glossary which is mostly used in by all flash array (AFA) vendors.

1)PE cycles
2)different types of flash available now
3)over provisioning
4)compression and Dedupe
5)garbage collection

PE cycles:the life expectancy of a flash drive is expressed in program/erase( PE )cycles. flash cells wear out a little every time they are erased or programmed. This is similar to erasing same spot of paper with an eraser multiple times which may result in tearing  of paper.

Different types of flash available now:below is the picture of different types of flash available as of now and their differences.

disks

Over provisioning:-This is the inclusion of extra storage capacity in solid-state drive. That extra capacity is not visible to the host as available storage. It is like under promise and over deliver .vendor will give you with more hidden capacity which will help in distributing total number of writes  and erases over more number of flash cells. This will increase life expectancy of drive.

Compression and Dedupe: There is a thin line of difference between dedupe and compression which most people fail to understand(including me.it took me reading multiple websites to understand it 🙂 ).

Dedupe: Dedupe occurs at file level. For suppose you sent a mail with an attachment of 1mb size to 10 people. The exchange server will save only one copy of attachment and mark remaining as duplicate.this saves a lot of space as we used  just  1mb instead of 10mb.

Compression: With compression you are using some algorithm or other to reduce the size of a particular file by eliminating  redundant bits. But if your users or applications have stored the same file multiple times, then no matter how good your compression method is your storage will end up with multiple copies of the compressed files.

Garbage collection:It took me some time to understand this.I will put it my way and provide you the links of blogs where I understood better.

flash writes data in different way. when we are trying to update data ,instead of rewriting in old cells, it writes in new free cells. This will make old cells data invalid or stale. Garbage collection is a process by which this old stale data is erased and make those stale cells available for next usage.You can find better diagrammatic explanation in wiki and also in some tech blogs in below links.

Link to understand garbage collection

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