Differences between hard disk SMR, CMR, LMR and PMR: Do you have anything to do with Linux?

Hard disk, Differences CMR, SMR, PMR

Well, the answer ráAsk TíTulo is No. But may not be así of all, but we must start at the beginning. And is that these téRoads LMR, SMR, CMR and PMR QuizáS listen to you every timeáS. Especially if it isás looking to buy a magnificent hard driveéTICO (HDD) and try to inquire about the TechnologyíAS to choose a good one.

Surely there will beás Seen that úLightly there is a lot of talk of technologyíto SMR for Modern hard drives. For example, Wester Digital, or WD, has released the LíNEAS Red Plus and Red Pro recently that are exclusively CMR, and has also hadéN that go out to deny problems with your SMR units. ¿But whaté are all these acronyms? ¿Qué Differences are? ¿They really have relationón or not with linux? All these questions tryé Clarify them

Differences between LMR, CMR, PMR and SMR

Dishes and hard diskhead

Head and Dishes: Seagate Medalist ST33232A

The first thing you should know is that HDD hard drives, that is, the magnificentéTicos or MECáNicos, USA Magnetism as a means to write and read The data on the surface of the discs.

Without going into too much detail of the compositionón of the dishes, and DEMáS Details, pass directly to differentiate the ways in which these memory accesses are performed. That is, the Types of MRS (Magnetic Recording) that exist:

  • Longitudinal (LMR): It is a type of data storage where you are stored longitudinally on the surface of the disc. The hard drivehead caná Magnetize one way or another (North-South) The AS areaí be able to create some and zeros for informationón binary. It is the CL formáSICA How the information was storedón on hard drivesáold.
  • Perpendicular (PMR): Seagate was one of the first to use this technologyíA for hard drives from 750 GB capacity. Teníto a clear advantage over MRL since, being perpendicular, each data occupied less space and could beíto store MáS InformationóN on the same disk surface. In additionás, it is heated less by retaining the info in areasás regular and stable.
  • Conventional (CMR): The rest of the manufacturers alsoén began using the PMR for your hard drives, so you end upó Bending the norm in this hard drive industry. That’s why it’s calledó CMR to be already extended and be the conventional. But it is the same as pmr.
  • SHINGLED (SMR): With the incessant struggle to get more data density by Centísquare meter, to be able to do hard drives with every time más capacity with the same amount of dishes and sizeñor, you thinkó TambiéN the technologyíto SMR. A type of recordingóN that differs from the previous ones for being staggered. In this type of technologyíA Small Size Reader Head is usedñor that the writing, and the data tracks overlap with each other. That increases the possibility of recording máS data on the same surface unit, that is, density grows. The problem is that it can be charged that a track is overwritten when trying to erase or modify a stored data, what to giveía place to corruptionóN data. The way to solve this problem is to write all the data that has to be modified in a separate sector and when there are downtime of the hard disk use, it is responsible for reorganizing the data. Something similar to what happens in the SSD with TRIM and the envelopeóN (overprovictions). But that has problems, since several scriptures should really be done when with other technologiesíAS should only be done 1 therefore, the increase in density in this case has a cost in terms of penaltiesón of the writing.

In short, in the úLtimum hard drives what is estatedán selling, be the brand that they may be,áto find you CMR or SMR. For instance:

  • Seagate: the barracuda máS new from 1TB to 8TB are usually SMR. While the Ironwolf tend to be CMR.
  • Toshiba: Many of your 1TB units to 6TB are usually SMR. Others like the X300, P300 and N300 tend to be CMR.
  • Western Digital: It has a very heterog varietyéNEA, with network series mixing SMR and CMR. The Pro network are CMR, Blue Mix, Black are CMR in its greatestíA with some exceptions, and Purple are CMR.

¿And whaté It has to do with Linux?

RAID, Linux Storage Server

Well, because the first thing is that Linux isá present in most servers, and alsoéN in a multitude of supercomputers. And these use configurations of RAID storage. Redundant systems do not get along too well with the SMR. At least, they should know if they have SMR hard drives or if it isán Mixed with other types of hard drives. Otherwise, you caníA generate serious problems.

Keep in mind that with RAID is used Scripture SimultáNea in several units at the same time. For example, in a RAID 1 (Mirror or mirror), everything that is written on a hard drive is writtenén in a b for así have an exact copy of the data and in case of failure of one of the units, have another backup

The Alterations in SMR caníto make these discs take too much to write data against the use of RAID systems only with CMR. However, there are RAID systems in which all their units are SMR and there is no too much trouble, but it is important that the staff Tétechnical dedicated to replacing units of a RAID system has a record of this.

There are práCosta, such as Dropbox cloud storage servers where nodes with SSDS and nodes with HDD SMR are used. But there is a trick, it is notáN together, but the SSDs are used as a buffer or cache to accelerate speed and when éSTOS have 1GB go by writing it in 4 blocks of 256MB of the HDDS. Therefore, they are complemented, but they do not mix

In fact, some people who have bought hard drives for NAS with configurationóN RAID and the new unit was SMR, VEíAn CóMo AppearíAn problems marking discs as degraded or seesíAn CóMo The reconstructionón late MáS of the usual when replacing an HDD unit on another.

But apart from the RAID system, there is another big problem for SMR, and is the XFS file system, TambiéN very employed in Linux environments. XFS is quite employed in NAS, and it produces that every time you want to rewrite a sector of 4KB Implique read and rewrite 256 MB complete. That causes the transfer rates totally disastrous.

ConclusionóN, for this type of technologyíAS RAID shouldíso avoid mixing SMR with CMR and for NAS dutyíace Avoid using XFS. But personally, I recommend you opt for the WRC and ASí Avoid limitations and headachers

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