With such early warning, one could make sure to have a spare drive readily at hand so that it can be swapped into the array on short notice. Having said all of this, it would be really good if there were a way to get early warning of the possibility that a particular drive might fail. But the same manufacturer might offer a so-called “NAS drive” which has a rated MTBF of one hundred years, for around $140. An ordinary 4-terabyte drive with a rated MTBF of five or ten years might cost $90. If you look around, you will find that the companies that make disk drives offer various levels of claimed reliability, for a price. And we order the two drives on different days so that they are not delivered in the same box (so that the two drives were not exposed to the same risks of damage along the way during shipment).
In our office we pick two different brands for the two drives. For this reason the person who is constructing a RAID array will take pains to ensure that the two drives in the array were not manufactured (for example) on the same day in the same factory (and thus might have in common some latent weakness due to something bad that happened in the factory on that day).
If there were some reason to fear that both drives might fail on the same day, then the RAID array would be no more reliable than any one of the drives. The alert reader will appreciate that this RAID concept delivers on its promise only if it can be assumed that with any two drives, the failure rates are uncorrelated. (Such a second drive failure, if it were to happen too soon on the heels of the first drive failure, would lead to loss of data.) The RAID concept permits the use of drives that are not so very expensive, while providing reliability that exceeds that of even the most expensive drive that money can buy. The further assumption is that if any drive within the array were to fail, the user will replace that drive right away before any second drive in that same array were to fail. The notion is that the loss of any one disk drive within the array will not give rise to loss of any data. The genius of RAID is to set up an array of two or more disks with clever hardware and clever algorithms so that within the array, any particular item of data is stored at least twice. No matter how much money you spend on a single hard drive, you will not reduce its risk of failure to a small enough level. You could attack this risk by saying that you will spend however much money is needed to construct a single disk drive that would have an acceptably low risk of failure during that interval.
#Synology disk health report re identification count how to#
The general question is how to reduce to a minimum the risk of loss of data due to disk failure during some specified time interval (say, five years). We start with the concept of RAID (redundant array of inexpensive disks). Imagine how one’s office would be brought to its knees, or worse, if a such electronic files were to be lost! Which brings me to the concept of monthly disk health reports. But I digress.) Being paperless, our important files are all maintained on file servers. We go through many reams of paper per week. Our office, like most offices these days, is paperless.