A little about data storage and experience 1cloud
The amount of data generated by mankind is increasing every year, and exponentially. This fact contributes to the development of new innovative technologies, thanks to which mini-revolutions occur periodically in the field of data storage.
To keep up with the ever-increasing demands of local and other storage, the capacity of hard drives is gradually increasing. We had 320 MB and 1TB, 4TB and 6TB drives. Now we have available industrial-grade hard drives with a capacity of 8 TB, the rotation speed of which reaches 7,200 rpm. HDD of such capacity are used in cloud technologies and corporate data centers.
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Note that hard drives must have high parameters of reliability, availability and performance. Perhaps, when you read the specifications of various disk devices, you met the phrase "Working height from -300 to +3 000 meters."
This is due to the fact that all disk drives require air to work, and its pressure inside the disk depends on the height at which the device is located — this need is incorporated in its design. The read / write heads should “float”, as it were, above the surface of smooth magnetic disks, which complete 120 revolutions per second.
In the book "Modernization and repair of PC" Scott Muller writes the following:
“Imagine this head: with such an increase, its length will be about 410 m, width - 325 m, and height - 100 m (these are approximately the size of a Sears skyscraper laid on its side). It moves at a speed of 9,187 km / s at a distance of only 5 mm above the ground (ie, above the disk) and reads data bits, the intervals between which are 2.16 cm. These data bits are located on tracks, the distance between which is only 29.9 cm
The speed of movement of this hypothetical head is even difficult to imagine, so I will give a specific example. The diameter of the Earth is 12,742 km, i.e. The length around the earth's orbit, which is one inch from the surface, will be approximately 40,000 km.
Thus, at a speed of 9,187 km / s, this head will make a revolution around the Earth in less than five seconds. In addition, the head will be able to read 231.33 Mbytes of data in one revolution around the equator. ”
In such a situation, the properties of the air separating the rotating surface and the read head are very important. For this reason, the developers of the device lay a certain range of heights at which the HDD will work without breakdowns.
Exceeding these standards significantly increases the likelihood of a read / write head failing - due to vibration, it may touch the surface of the disk. If special holes were not made in the disk drives for air circulation, the upper and lower plates of the disk would have to be weighed to compensate for the effect of pressure changes.
Almost all disk drives have such air ducts.
However, there are exceptions to any rule - not all disk devices have “breathing holes”. For example, in 2013, HGST (Hitachi), a subsidiary of Western Digital, was able to fit seven 3.5-inch drives (6 TB) into one HDD, using a sealed helium-filled camera.
Since helium is 7 times lighter than air, when using it, changing pressure is not a problem. To keep the gas inside the sealed chamber, laser welding of seams was used.
A helium hard drive at 7200 rpm is about 4–5 degrees colder than normal (since the thermal conductivity of helium is an order of magnitude higher than air), and consumes 33% less electricity. Due to this, data centers have the opportunity to increase disk density, which means lower operating costs and a reduction in the space occupied by devices, compared to classic systems of similar capacity.
A little later, HGST released a 10 TB hard drive, surpassing the characteristics of its rival Seagate (8 TB drive). By 2017, the company plans to fully switch to the production of disks with helium, abandoning the "air" hard drives (other technologies that can turn our understanding of storage can be read here and here , and here ).
SSD drives, which are non-mechanical storage devices, are also spared from problems with pressure drops. Recently, solid-state drives, mainly due to the high speed, are used in data centers. There are arrays, built entirely on flash memory, and hybrid arrays that combine solid-state drives and hard drives.
Here the user has to choose what is more important for him. SSD offered breathtaking speeds and very high cost per gigabyte. On the other hand, multi-terabyte hard drives are much cheaper, but, having a speed of 75-100 IOPS, can not cope with a large load.
Hybrid arrays are a kind of compromise. Adding flash memory in the amount of 2-5% of the total memory, you can almost double the number of IOPS, which will reduce the latency of the system to 3-5 ms (without flash technology, it is more than 10 ms). Thus, by paying only 10-20% more, you can double the performance of the array.
Users of the 1cloud service can now also connect different disks to the same virtual server. The simultaneous use of different types of storage devices makes it possible to make the overall infrastructure solution more flexible, efficient and cost-optimized.
The development of new functionality did not take much time and was accompanied by a standard process of making changes: the refinement of the control panel interface and the external site. To add a new disk, the user only needs to go to the control panel of the virtual server and, following the tabs Settings -> Disks, add the necessary devices.
Disk space is provided from NetApp FAS6240 / FAS8040 arrays. At the vCloud Director level, separate storage policies are organized for each type. Starting with vCloud Director version 5.6, it became available (but only through the API) to change the storage policy for specific drives.
To implement this functionality, we had to patch the .net SDK from VMware a little because of a detected error, when, when adding an additional disk, the SDK tried to create another bus with a null identifier.
Below is a code illustrating the correct settings for adding a virtual disk:
VirtualDisk vDisk = new VirtualDisk(10240, BusType.SCSI, BusSubType.LSI_LOGIC_SAS); vDisk.GetItemResource().Address = null; vDisk.GetItemResource().AddressOnParent.Value = unit.ToString(); //unit number, vDisk.GetItemResource().Parent.Value = bus.ToString(); // Despite the growing popularity of SSDs, it is still early to completely abandon the HDD. It is very reasonable to use different storage devices for different types of tasks.
For example, an actively used database should be transferred to an SSD-drive - this will optimize its speed, but it is logical to leave the operating system on slower SAS-drives. To store backups, you can even connect a slower, but larger in size SATA-drive.
PS Other interesting materials on the topic:
Source: https://habr.com/ru/post/278055/
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