11.10.10

What there is to know about SSD`s

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New technology is fun. We get new opportunities, new gadgets and new knowledge to put us in. And since we last week took a look at a few potential candidates for your first SSD - Solid State Drive, it is time for a little dip in the mysterious world MemoryDisc.

The more you already know about hard drives and memory technology, the easier it will be to understand how an SSD works. So since not all start at the same level here, we'll start easy and gradually becomes more sophisticated over time.

A SSD is a hard drive from an overall perspective you can think of a solid as any "normal" hard drive. It uses the same file system, and the operating system thinks mainly on reading and writing files in the same way as with the old hard drives. But under the surface there are fundamental differences in the way they store and read data. The conventional hard disk reads and writes from / to the rotating magnetic discs, while an SSD uses memory technology and works a bit like the computer's internal memory (RAM). But for its part, the internal memory disappears with the information once power is gone, while an SSD uses so-called flash memory, which also keeps the data even if it is not connected to a power source. Flash memory is also including the so-called flash drives and memory cards for digital camera or mobile phone.


Operativsystemet ser egentlig ikke forskjellen på en SSD og en hvilken som helst vanlig harddisk. Foto: Seagate
An SSD has no moving parts, a conventional hard drive stores data as mentioned in rotating disks, and does this with tiny read / write head that sits on the end of a mechanical arm. When the disk rotates the head hovers about three nanometers above the disk, which is very small - a typical human hair is hundreds of thousands of nanometers thick. Now perhaps you understand why you should not open the disk - even the smallest particles can literally clog the machinery owned.

With such small margins, it is no wonder that accidents can happen, for example if you lose your laptop on the floor when you work with it. And in addition to the risk of read / write head to scrape down the plates have the things with moving parts are generally easier to break. Having said that hard drive manufacturers have now had a few decades to nærtil perfecting their art, so today's drives are very robust, all things considered.

But the fact that an SSD has no moving parts is much more to say than that it only becomes more robust. When a normal hard disk to write or read a file using it a long time to find the right space on the disk - the mechanical arm must be moved and must wait for the disk has rotated to the right point. This has especially to be read and / or written to many different parts of the hard disk.  
Ytterst på armen sitter det lille lese-/skrivehodet. Foto: Shutterstock
At the end of the arm is the small read / write head. Photo: Shutterstock 
An SSD does not need to wait for things to move, giving it a big advantage in terms of response or access time - ie the time from when the computer asks for data to be read or written to it actually happening. Especially when the disk to write many small files is a solid superior to a conventional hard drive.

That a SSD does not spin that it uses less power than a regular disk, but here it made great strides in recent years. A modern 2.5-inch mechanical disk uses only marginally more power during normal use, and the difference in weight is not something to talk about.


An SSD can not live forever
flash memory used in most SSDs are the type of MLC (Multi-Level Cell), and can be written over about ten thousand times before risking spontaneous memory problems - with age will thus run the risk of a forgetful SSD. A faster, better and more enduring is the SLC flash memory (Single-Level Cell), which can withstand up to hundreds of thousands of projections. But this is also considerably more expensive.

Most SSDs aimed at the consumer market is the type of MLC, which means that you can not expect your new SSD will last forever. But there is no reason for immediate panic, because the disks have algorithms that try to prevent the same memory areas on an SSD is used again and again - rather than the disk's controller try to keep the "wear" as smooth as possible over the entire disk. So even though 10,000 of projections sounds quite little, we still talking about a lifetime of up to several decades. Once your new SSD park slippers, a far less expensive, larger and better technology to be ready.


The SSD shall not be defragmented!!!!!!
to write to or read from a rotating disk is naturally the fastest if this is done sequentially - that is, the data is located after the other on the plate so that the read / write head does not need to move physically to read the next sector. On a typical hard drive, it is therefore customary to collect (fragments of) the data that is scattered around the hard disk. This is called defragmenting.


Farvel til defragmentering - som vi uansett aldri var spesielt flinke til.
Farewell to defragmentation 
no matter that we were never particularly good at. For an SSD it is perfectly normal to spread data around on disk. Reading from or to a given memory location does not take a shorter or longer time than another, and is mentioned in the disk's nature to ensure as smooth as possible wear.

Another reason not to lump data together is that SSD's major strength is being able to read and write to many different parts of memory simultaneously, in parallel operations. This is why we genererelt can say that the larger the SSD, the better the performance.

A SSD like TRIM
There's no need to worry about defragmentation does not mean that it is indifferent to how data is entered and stored on an SSD. The problem lies in the way they treat the deleted data - like regular hard drives are in fact no data is removed from the solid-state one when you delete a file. Instead, the area lies on the data considered writable by the operating system. It is this that makes it possible to save deleted files.

But while conventional disks can overwrite a file directly, it is not as straight forward with flash memory technology. The memory must in fact be deleted before it is written to again, nor it is as easy as it sounds.

If you have some knowledge of regular hard drives do you know the more that it is divided into sectors, which is the smallest amount of data that can be printed. So it is a SSD - but here this is called a page and is usually 4 KB, ie 4000 characters. 128 of those pages of 4 KB is grouped in blocks of a total of 512 KB.

It is easy to read data from a particular page, and write to a blank page in a block. But to overwrite a page is therefore not, it must first be deleted. The big problem is that an SSD can not delete a single page, either. It can only delete the whole block, that is, all 128 pages or anything.

This means that when the disk begins to be well used and the blocks have filled the pages with all sorts of different data, the write performance get a break. Instead of being able to write directly to a page, first the entire block is read and stored in the cache, then the current block is deleted from the solid-state one, block in the cache must be updated with the new page, and then whole lot written back to disk . It takes you realize a lot of extra time.

De fleste nyere SSD-er, som disse, støtter TRIM. Noen eldre modeller lar seg også oppgradere til å gjøre det. Foto: Vegar Jansen


A kind of solution here is a command called TRIM. This allows operation in the above section is performed when you delete files, and not only when the disk is busy with a lot of write operations. In order to turn into TRIM is required that this is supported by both solid-state one (most new models do this) and the operating system - in practice, when we talk about Windows 7 or Linux 6.2.1933 (Mac OS X will probably support the upcoming TRIM version).

Do you have another operating system, it is good to know that there are tools that allow you to run TRIM manually, such as Intel SSD Toolbox if you have such a disk. Do you have another SSD should check the manufacturer's website to find out which solutions exist.

But remember that is that TRIM has the disadvantage (or advantage, depending) that you can not restore the data back if you accidentally to delete an important file.

A SSD like probably AHCI 
Advanced Host Controller Interface is a software interface developed by Intel for SATA controllers, and has some extra functionality compared to the standard SATA / IDE standard. For more SSDs, it is recommended to run the motherboard controls Achi mode (or the Intel RAID controllers) to, among other things, to read the data with multiple prossesstråder. But when it is said there is no really difference in practical use, and Achi are not required for TRIM to work.
AHCI kan velges på de fleste moderne hovedkort.
AHCI can be on most modern motherboards.
 
If you are unsure, you should first check if AHCI is recommended for your SSD. If so, you can turn this into your computer's BIOS, and you can benefit from taking a look at the manual if you are relatively fresh. Note that to go straight from IDE to AHCI mode may result in blue screen, if so is it greiest to make the transition during a reinstallation.

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