I'm a computer developer by trade.
I have never heard of SPARES in relation to a hard disk drive. Sure, there is a Sector 0; sure, you don't want that going out.
But I have no Earthly idea what SPARES is, unless you mean a spare drive. And spare drives are cheap.
So, explain your concern, and do so technically, or I will assume you are a technical dolt.
(PS: 99.99999% of the time, almost all your data is recoverable. You may have to pay a pretty penny to get it back, but it is recoverable in the vast majority of cases.... even if your boot and other important sectors go out.)
They are built into the low-level drive formatting. Your hard drive swaps it in, when it see a failing sector.
OSes do another level on top.
I just saw this banner ad when I was searching Pinterest for quiche recipes. “Fix your hard drive by doing this one weird trick.”
Yes, all Drives have Spares. And Yes, all Hard Drives and Non-NMVe Solid State Drives have Spare Sectors to replace suspect ones. On NVMe Drives it is Spare Blocks instead.
These Spares are in reserve above the the original size of the disk so you loose none of the capacity when used.
Todays drives spare automatically, when the error in the Sector or Block (NVMe) is corrected via Firmware the data is written onto a Spare instead, and the errored Sector/Block is marked suspect; not for use anymore. The reason for this is that the next time around, if the Sector/Block is not spared, AND that Sector/Block is now UNCORRECTABLE, it may cause a critical function or program to fail when the error is reported.
On Hard Drives today, when a sector is spared, the user may see a short delay depending upon the retries allowed in firmware. There generally is no notice given to the user that this is occurring. The Spare sector comes from the SLOWEST PART of the Drive nearest the Spindle.
On SSDs/NVMe drives, the sparing occurs virtuously instantaneously. With no delay to be seen or reporting to the user. The spares are as good as any other sector/block on the drive speed wise.
Scheduled Defragging (for hard drives), reallocates the data on the spare sector used, back to a faster part of the Hard drive along with the data on the rest of the file and sets the spare sector used to the end of freespace. Thus helping the Hard drive to work better.
The Spare sector table and it's count, on a Hard Drive is generally known as a G-list.
https://www.dataclinic.co.uk/hard-drive-defects-table/
BUT SCHEDULED DEFRAGGING and WINDOWS FILE INDEXING ARE VICIOUS ENEMIES OF SOLID STATE C: and busy NVMe Drives. TURN THESE OFF for SSDs and NVMe Drives NOW!!
SSDs and NVMe drives depend on Non-Volatile Memory which can be written to, only so many times before it starts to error. I've heard this to be about 66 thousand times at the worst.
To fight the low writing capacity, SSD/NVMe drives use Smart Write caching and sneaky write distribution methods, to reduce the impact of excessive writes on these drives.
On NVMe drives, the spare table may be known as as the "Available Spare Threshold" count and table: https://advdownload.advantech.com/productfile/Downloadfile3/1-1YX8KBB/SQFlash%20SMART%20ID%20Definition(NVMe)_v1.1_20200922.pdf"
Available Spare Threshold: When the Available Spare falls below the threshold indicated in this field, an asynchronous event completion may occur. The value is indicated as a normalized percentage (0% to 100%).
When the "G-list" for hard drive and Non-NVMe drives run out, THAT'S when KABLAM can happen. Or the "Available Spares Threshold" count is ignored and goes to Zero...
And the Majority of you are Right. Most wise businesses use RAIDs or spare backup system disks. But there is no RAID in for Smartphones/Smart Watches/Ipads and most general PC users as most do not know alone, or why one would want it.
Yes the Dirty Ticking Time Bombs are out there. The good news is that the drive manufacturers are starting to report the Spares data in a way that can be meaningful and eventually useful to Operating systems to catching the TIME BOMBS before they Go OFF.
For as far as I know, the only way, today, to see the G-Lists and AVAILABLE SPARES list is with manufacturers software. Any of you knowing Operating Systems that can see these and do anything with the data now, PLEASE LET ME KNOW.
Few know about spares and generally what they know about them is far from reality.
Thanks.
A very Old Computer Tech that has waited for this day for a long time.