Should we leave a certain amount of free space on a new harddrive to help longevity?

I know technology is getting better and better over the years but I was just thinking, what is an ideal amount to leave free space in order to help make a HDD last its full potential… I have also thought I should leave about least 1.5TB free or so out of 10TB or does it even mater (now a days)?

Performance degradation in relation to capacity utilization is primarily a concern for SSDs rather than traditional HDDs because of the way data is written to NAND flash, with exceptions such as Intel’s Optane. Most manufacturers actually build in mitigations today, such as reserved spare space in the NAND flash.

Either way, unless you’re gonna fill up your disk to 99%, or you’re running applications that are super-sensitive to disk performance, I wouldn’t worry about it. More of an organizational concern than a performance concern.


Leaving space on spinning rust has no effect on the fact that it’s likely to die from the motor bearings failing or some vibrational consequence. Where it could have any effect would be on the filesystem applied to it. NTFS (as one example) has metadata needs aside from the space for your files, BUT it will generally pre-allocate enough space for the MFT when the disk is formatted, and you would have to significantly increase the number of files over time to cause the MFT to need to grow. Even then, all that would happen, is the filesystem would “lie” and say it was full when it was not, if it wasn’t able to grow the MFT in order to store an additional file.

If its your primary OS drive, you need to have room for patches to be downloaded and applied, as well as for “checkpoints” (temporary system file backups) and other such things. If this is what you were thinking, then your suggestion to leave 1.5TB free on 10TB is not bad, but may be overkill. (My Windows system SSD is only 500G and I only have about 50G free and am not having any issues.)

As @knewman mentioned, you definitely would prefer not to operate a SSD completely full because it needs free space to do the internal maintenance it wants to do when performing wear leveling (which maximizes the life of your SSD’s flash cells.)


For spinning rust, it is more the application you are using it for (primary OS partition, data storage, backups etc.) that is important.

If you have an OS on it, you need to keep at least a few GB free for it to store temporary files and space for updates and to defrag itself (if the file system requires it). We usually keep at least 10GB free on our system partitions on our virtual machines, for instance.

If it is data and the data is being expanded, then you need to keep enough space free for the data to grow and be able to buy an additional drive, before it fills up. Monitoring the data growth and setting an alarm by 10% is a usual rule of thumb.

If it is a backup, then it needs to just be a few bytes bigger than you data set - although the OS and backup software will often panic and claim the drive is too small. Again, a couple of GB more than you need is a good idea.

As the others have said, SSDs are different, but for different reasons. The fuller an SSD becomes the slower it becomes at writing and it reduces the life of the drive. SSD is also poor as a backup medium, because the NAND cells will slowly loose their capacitance over time, when not powered on.

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OK thanks for the reply, I was referring to a HDD for backup mostly but thought would apply to OS also… I just thought leaving extra space like 1/10th would help it defrag better…even though I think I remember Leo saying we don’t even have to defrag HDD as much as we did15-20 years ago…

To be honest, I hadn’t considered defragging. If you’re actually updating the data on the drive often (i.e. replacing files, deleting files adding new files) then a defrag now and the may be helpful. On the other hand, defragging isn’t that helpful if the files aren’t being regularly accessed… the overhead of skipping from fragment to fragment only really adds up with many usages. (Since OS files are such files that are usually accessed often, defragging your OS partition (if it’s a HDD and not a SSD) can be important.)

If you do want to defrag it on occasion for whatever reason, then your logic is probably correct, having some extra space can be helpful when defragging. (It’s not strictly necessary, but it should speed up the degrag, and make it safer (because less data will be held temporarily in RAM because there will be more room for writing a second copy so you can replace the first copy.)

Edit to add: Since your original post was about longevity, it should be noted that stressing the drive out doing “needless” defrags is probably not adding to longevity, unless it’s really badly fragmented.