Hello, I’m Christopher, and I’m the Director of Customer Relations here at Covecube Inc. For those that may not recognize me, I have been very active in the Windows Home Server community, where I usually go by the username of “Drashna”. I have even been awarded the Microsoft MVP Award for Windows Home Server for the tech support I’ve provided in the forums and how-to guides that I’ve written for Windows Home Server.
We tend to get a lot of questions about the StableBit Scanner, what it does and some of the values that it presents. So let me try to answer some of those questions here, and explain a bit more about what the StableBit Scanner does, and why it’s a great utility for maintaining the health of your disks.
I will apologize now for for the amount of text here. There is a lot of information that I want to cover, and I don’t want to skim over any of it. So if you will bear with me, let’s cover exactly what the StableBit Scanner does, and why you should install it.
First, lets talk about the SMART data that the StableBit Scanner is able to pull from the disks. This data is pretty much universally accessible on any drive you can buy, whether it’s a “spinning” hard drive, or if it is a Solid State Drive. Most of the information is pretty standard, but there are some more device specific values depending on the manufacturer of the device. And there are plenty of utilities out there to read the SMART data from your disk. For the most part, they all read the SMART data from the disks and interpret that data in a meaningful way for users. Some just show the raw output and let you know if the values are outside of manufacturer specification.
Let’s talk about some of these SMART values and what they mean for your system. It’s always a good idea to know what’s going on.
- “Reallocated Sector Count” and “Reallocation Event Count” is probably the value that you will see increasing most often. What this means is that the disk has detected an issue with a bad section of the disk, and has reallocated the sectors to a special reserved (spare) area on the disk. This happens automatically, and prevents the disk from using these spots in the future.
This is normal, and typical on a HDD and one or two appearing once in a while isn’t necessarily a bad sign. However, if you see this value rapidly increase on a disk, or you have a lot of them, then there may be damage to the physical medium of the drive and you may want to replace it immediately.
Though, as this value increases, the performance of the disk may be adversely affected. The remapped data will be at another location on the drive, causing the read speed to be decreased due to “seek time” for the new location. And the more Reallocated sectors you see, the more that this will happen. So if performance is very important, it may be worth replacing the drive sooner rather than later.
- “Spin Retry Count” is a value only found on HDDs, obviously. It shows the number of times that the drive has failed to spin up to full speed and had to retry to spin it up. This indicates a serious mechanical failure of the platters. There are a number of possible causes, but none are good. It means that you should remove the data from the drive immediately and replace the disk.
- “Current Pending Sector Count” and “Uncorrectable Sector Count” – These two values tend to go hand in hand. These means that the disk has encountered issues reading from the drive. In fact, if you force a surface scan at this point, you may end up with the same number (or more) sectors as indicated by this value. The drive will attempt to write to these sectors eventually, and when that happens, it’s either able to and clears this value for that sector or it fails and forces the disk to remap the sector. By “remap”, I mean that this will trigger a “Reallocated Sector Count” increase. This all happens automatically in the course of normal usage. Things like a full format, writing zeros to the disk, or utilities such as SpinRite try to force this process to happen quicker.
- “Load Cycle Count” – This is a value that we get asked about a lot and one that can rapidly increase. Specifically, this is the number of head parking cycles that the drive has performed. Parking the heads is a normal process of the drive, and helps prevent accidentally damage to the drive. This occurs when the drive idles. Depending on how this is configured on the drive, and how active the drive is, this can grow very slowly or can increase by 100 or more in a single hour. Western Digital Green drives are particularly notorious for being poorly configured and rapidly increasing the count.So this is a value that should be taken with a grain of salt. Watch it yourself, and if only slowly increases, then you may be able to trust that it’s accurate. And in that case, it may be a good indicator of age and usage. However, this value doesn’t necessarily indicate an issue. It’s much like the “Power on hours” or similar statistical information.
SMART data can be a good indicator of mechanical problems, however, it is reactive technology, for the most part. It’s designed to predict immediate failure, and it can’t predict into the future the exact point in time at which the drive will fail, and it’s not designed to. It’s akin to klaxons on a ship, letting you know that something is wrong, and to scramble to fix the issue.
That brings us to the next subject.
Now for the “blood and guts” of what the StableBit Scanner does.
By default, the StableBit Scanner is configured to do a surface scan of the disks in the system. What do I mean by a “surface scan”? The StableBit Scanner does a sector by sector scan of the entire disk, ensuring that each and every sector on the drive is readable. And when it finds sectors that are not readable, it flags them and keeps on scanning the rest of the disk.
Now, why is this important? Because after time, the “bits” on the disk may degrade. Over time, if the data is not accessed at all, it can lose it’s stored state and this is what is referred to as “bit rot” usually (different from “random bit flips”). By reading this, it gives the drive’s onboard diagnostics tools the opportunity to repair the section, or just remap it if it needs to, before becoming an issue. This process is called “Data Scrubbing“, and helps your disk identify potential problems before they affect your data. This can be noticed by changes in the SMART Data values on the drive (such as the lowering of the uncorrectable sector count, or an increase in the Reallocated Sector Count).
Wear and Tear
Though, there is a good question that has been raised to us at least a couple of times: Does this surface scan put additional strain on your disks?
For Solid State Drives? Absolutely not. They are designed to be read from many times without any degradation of the drives.
For conventional hard drives? That’s not as straight forward. But basically, any time the drive reads or write data, there is a chance of damage occurring. However, modern drives are very, very good at preventing this from happening.
The other concern here would be wear on the mechanical parts of the drive, the parts that spin the patters, and the parts that move the read/write heads. By default, the StableBit Scanner is configured to do this intensive surface scan every 30 days. What does this mean for the disk? That it’s reading the entire surface of the drive, the full capacity of the disk, once a month. That’s a good amount of work for the drive, and that will happen often.
Well, what if I scan a 3TB drive once a month? That’s about 35TB read in a year. Once a week? That’s about 140TBs read in a year. Okay, that’s a lot of reads over a years time. However, how does that compare to normal usage? Well, do you backup the drives? If so, the entire contents of the disk are read, or every sector is read, depending on the backup utility. What about Windows Search? Or Previous Versions? Or how about streaming from the disks? And how often does this happen? Well, that really depends on your usage.
And to get some perspective here: I have several 3TB drives in my system, that are getting close to 2 years old. I move data around a lot. So what do my drives look like? Well, most report in the ballpark of 50-100PBs of reads and writes. That’s PB (petabytes). Each Petabyte is about 1000 TBs. So thats 50,000-100,000 TBs of reads. If I scan once a month? That’s not even 1% of the total reads from the disk. And while I may not be a typical user in a lot of ways, it should give you a good idea how little of an impact these surface scans have on your disks. And disk are designed to last years, even under heavy usage.
Now what are these damaged sectors that the StableBit Scanner finds and what does it mean to you?
Damaged sectors are bad sectors on the disk that the Surface Scan has issues reading. It means that… well, that it is likely damaged, and during normal operation, you may get an error accessing affected files (or even experience file system errors). These damaged sectors are the same ones that are identified by the “/r” switch on the CHKDSK utility.
Now, you may be asking yourself, why run StableBit Scanner and let it recover that data instead of CHKDSK? Well, you should and shouldn’t. It depends on what you want to do.
- CHKDSK does a “best effort” to recover the data. It attempts to read, and then move the data. However, once it determines that it can’t recover it, it reallocates the bad sector and makes that data unrecoverable. And depending, it could potentially corrupt the data, or even lose sections of it.
- StableBit Scanner cares about recovering data firs and foremost. Once it’s identified damaged sectors, you can run a “file scan” which attempts to figure out what was damaged on the system and what files are affected. Then it lets you attempt to recover that data. In fact, StableBit Scanner uses 20 different “head placement profiles” to attempt to read the data. This is a lot more aggressive that the CHKDSK utility’s attempt to read the data.
- StableBit Scanner does not repair this damage on the disk. If it fails to read the files and cannot recover that data, you can still run a data recovery utility to attempt to recover that data as well.
- Again, if you run CHKDSK with the “/r” flag, it fixes the sector by reallocating it, meaning that you lose the ability to ever recover this affected data. This is because the data has been overwritten or the location remapped. So the data is no longer available for recovery.
All in all, the StableBit Scanner is a great tool to inspect and maintain the health of your disks, and the data that is on them.