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NAS (Network Attached Storage) are becoming more and more popular and the question of which drives can be used in them is becoming more and more relevant. After all, the reliability of data storage in RAID1-5 is already much higher than that of a separate disk, so is it necessary to overpay for some special disk? What is RAID Ready – a marketing ploy, or something useful? The answers are in this article.

Working conditions
First, hard drives do not like vibrations – they can affect the head unit and slow down the read or write speed. Secondly, hard drives themselves are sources of vibration. The first has nothing to do with the second, as long as there is only one disk in the system. But if several hard drives are located side by side on the same hard chassis, the vibration of some HDDs begins to affect the operation of others. Therefore, RAID Ready drives have special measures to reduce vibration.

HDDs prepared for RAID are more precisely balanced, minimizing vibration due to pancake imbalance. In addition, RAID Ready drives are equipped with vibration sensors that transmit data to the HDD controller. Based on this data, the controller can change the drive mode to reduce vibration.

Temperature The
hard drive can become very hot during operation, up to 55ºC or more. For a desktop drive, this is not critical – usually the internal ventilation of the case is enough to maintain the temperature of the drive at an acceptable level. It is a completely different matter when several disks are fixed close to each other with almost no air gaps and in a small case. Heat dissipation in a NAS is much worse than in a spacious desktop case, and “hot” drives can quickly fail due to uneven temperature deformations.

RAID Ready drives use energy-saving technologies to reduce heat generation. Many of these HDDs can change power consumption (hence heat dissipation) depending on the load. And even if the RAID Ready HDD overheats for some reason, the NAS controller will not allow it to be damaged by disconnecting the disk in time and displaying an error message.

Nature of work
Hard drives have long become quite smart devices – their controllers are able to optimize the operation of disk mechanisms, depending on the mode of operation of the rest of the periphery. But the nature of work in the desktop and NAS is different, so what is optimal for the first will be completely useless in the second.

For example, parking the block of heads in the absence of read-write operations. This is a common option for desktop disks, which significantly increases the safety of data on the disk. In the parking position, the heads are displayed beyond the edge of the “pancakes” of the disk. Then an accidental shaking of the computer no longer causes the heads to touch the surface of the “pancakes” and damage them.

It’s just that extra milliseconds are spent on parking and returning the heads back, slowing down reading and writing. For NAS, this can be critical, so RAID Ready drives either do not park their heads at all during operation (only when turned off), or the parking timeout is configured by the NAS controller.

The same applies to stopping the disk. This option is more common in laptop 2.5″ drives – when idle, the drive stops completely, saving electricity. But it takes an unacceptably long time to spin up – up to a second.

Why are delays bad when using an HDD in a NAS? Firstly, it reduces the overall read-write speed, depriving the NAS of one of its main advantages. Secondly, in a NAS, the inactivity of one disk does not mean that the rest of the array is also “idling”. In such a situation, the “sleep” of one disk may be a signal to the NAS controller that it is malfunctioning.

What happens when a read/write fails
A separate hard drive does not have any data redundancy. If the information is not read, it is lost. Therefore, the desktop hard drive tries to read the failed section “all the way”. With the characteristic crackling of recalibrating heads, the drive will repeat and repeat read attempts until it can read the data or gets a “hang up” from the system.

NAS has a different situation – the data is reserved, a single failure is not a problem. But reading delays are bad. Therefore, after waiting for a certain timeout (usually 8 seconds), the NAS controller rejects the failed disk and “throws” it from the array.

For desktop hard drives, it is rarely possible to set the time during which the drive can try to correct an error. Although this parameter is written in SMART (hard drive self-monitoring technology), most often it is either absent for desktop drives or unchanged and set to 0/0 – which means unlimited time to try to correct both failed reads and writes.

For RAID Ready drives, this parameter (SCT ERC) is, firstly, different from zero and rather small, and secondly, it is adjustable and can be adjusted to the parameters of a particular NAS. For this reason, when using a single RAID Ready disk, it is recommended to set SCT ERC more, for 3–10 s, otherwise the risk of data loss increases.

SMART (Self Monitoring, Analysis and Reporting Technology) appeared in hard drives more than 20 years ago, but its analysis and reporting capabilities are poorly used in home computers. Therefore, the implementation of SMART functions in desktop drives is often far from perfect. The data in the SMART table may not correspond to the actual state of affairs on the disk, some models have noticed data loss in the cache when accessing SMART, etc. But in the past, this was of little concern to both users and manufacturers.

Everything changes when the hard drive is installed in the NAS. The NAS controller frequently monitors disk performance and evaluates changes over time. Based on this data, the controller draws conclusions about the reliability of the disk and its current state. If the SMART functions are implemented incorrectly, the NAS controller may immediately, or over time, “reject” an absolutely healthy drive.

RAID Ready drives not only have SMART working correctly, but sometimes use advanced monitoring technologies. For example, IHM (“IronWolf Health Management” – “Health Control” of Seagate IronWolf hard drives), which controls 10 times more parameters than SMART. This allows you to diagnose emerging problems with the disk in advance and take actions to protect data.

What is SMR and why is it bad
Not to say that SMR (“Shingled Magnetic Recording” – “Tile Magnetic Recording”) is definitely bad. The technology allows a significant increase in the volume of hard drives while maintaining other characteristics and in some cases can provide good savings without any harmful consequences. But not when used in a NAS.

The write head of a hard disk is larger than the read head. “Tiled” recording is based on the fact that the width of the disc track is made in accordance with the size of the reading head, and not the writing one. This allows you to place many more tracks on one “pancake”, significantly increasing the volume of the disk. True, when recording, you have to rewrite overlapping tracks (they seem to overlap each other, which is why the technology was called tiled).

In order to avoid speed losses during recording, SMR disks are equipped with a fast disk cache – ordinary tracks of normal width located along the edge of the “pancakes”. When writing, data is first written to the cache, and then, when the load on the disk decreases, the controller rewrites the data to the main place. But this only works as long as there is no need to write a large amount of data to disk.

In principle, such disks can be used as part of RAID arrays, but only RAID 0 or 1. In RAID 5–6, when the array is rebuilt, the cache of SRM disks quickly overflows and write operations slow down many times, which often leads to their rejection by the NAS controller.

RAID-Ready drive lines
Each manufacturer has its own line of drives prepared for NAS.

Seagate has the IronWolf line .

Vibration reduction is provided by AgileArray technology, which includes careful balancing of drives and constant monitoring of sensors to prevent resonance and reduce vibration. To optimize power consumption, PowerChoice technology is used, which allows you to choose one of four stages for the drive, depending on the load. Diagnostics and health monitoring, and early detection of drive problems are provided by IHM technology, supported by most NAS manufacturers.

SMR is not used in IronWolf discs.

Western Digital
WD recommends red series drives for use in RAID arrays.

To reduce vibration, WD Red uses 3D Active Balance Plus technology, which allows you to balance disks directly during operation, preventing vibrations from increasing. NASware technology is responsible for optimizing the operating mode depending on the load.

Some WD Red drives use SMR technology and are not recommended for use in RAID 5/6 NAS.

Toshiba’s NAS line has the N300 index.

Toshiba Stable Platter Technology, used on the N300 drives, stabilizes the drive shaft during operation based on vibration sensors. The company does not disclose the manufacturing technology of N300 drives (SMR or CMR), but independent tests give grounds to state that SMR is not used in N300 drives.

As can be seen from the above, the use of RAID Ready drives in network storage is more than justified. Installing regular drives in a NAS can lead to slower read/write speeds, hardware errors, and even drive damage, especially if the array is large.–j-robert-oppenheimer-621fa33092072a6b5cd6b427


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