I have Adata su650 480GB SSD which is generally working fine. Recent check of SMART values using CrystalDiskInfo reports 257 bad block count. Now I need to know a few things with respect to this parameter

  1. What is this bad block count and is it early or later bad blocks?
  2. Does it mean 257 blocks are bad?
  3. Are they excluded from I/O after being reported?
  4. Sometimes when copying a single large file, the speed drops to just 2 – 3 MB/s for a few seconds and then again jumps to 200 MB/s. Is this because of bad blocks?
  5. There’s no visible data loss as of now. Nothing seems to have gone corrupted
  6. Do I have a bad SSD?

CrystalDiskInfo screenshot

Thank you all for informative answers.

Response to comments –

I have double checked with Adata SSD Toolbox but the parameters like Reallocated Sector etc are not reported. Maybe they are missing in the hardware itself.

Further investigation-

I downloaded Adata’s SSD Toolbox app and it reports these parameters as Vendor Specified. See the attached screenshot:

AA Vendor Specified 72 72 10 Raw Value 101 Hex

That’s puzzling. Does it mean CrystalDiskInfo is interpreting the data and reporting it differently? Is that Bad Block Count really Bad Block Count? I would trust Adata’s tool as they know what they have designed?

I tried submitting online query to Adata Support online but the web form errors out in the end

Adata SSD Toolbox screenshot

This question may appear to be a duplicate of Bad block count (early - later)?, but here I do not have early or later separation of data, so this is not an exact duplicate as such, and I have a larger scope.

  • 1
    Bad blocks are normal with SSDs that the reason spare blocks exist
    – Ramhound
    Nov 23 at 21:14
  • 1
    I don't see 05, C5, or C6 (reallocated sector count, current pending sector count, and uncorrectable sector count). having more than a handful of any of those indicates that the disk at least need maintenance, and depending, may be failing. Nov 23 at 21:43
  • @FrankThomas Indeed, but depending on the vendors not all the attributes are reported.
    – PierU
    Nov 24 at 6:44
  • 1
    S.M.A.R.T. is an impressively bad standard. Vendors have a great deal of freedom to interpret it in a manner profoundly different from each other.
    – fraxinus
    Nov 25 at 9:00

4 Answers 4


Your SSD is in excellent shape and has no problems.

SMART attribute AA (170) is named by CrystalDisklnfo as "Bad Block Count", but other sources call it "Reserved Block Count" and define it as:

Reserved Block Count S.M.A.R.T. parameter indicates a number of reserved bad block handling. Recommendations

Although this parameter is not considered critical by the most hardware vendors, degradation of this parameter may indicate electromechanical problems of the disk.

Another description by Kingston says rather:

This Attribute is related to attribute 5: Retired Block Count. It provides a count of reserve (over-provisioned) blocks. (Note that all blocks, including reserve blocks, are in service at all times; reserve blocks constitute Flash memory space over and above the drive’s logical capacity).

The Attribute value is initially the total Reserve Block count. The value is decremented as the reserve block count diminishes over the drive’s life.

It's basically the number of good blocks that are available for mapping bad blocks, or in other words replace a bad block by one of these blocks. The number goes down, not up, as bad blocks are encountered. When it reaches zero, the firmware may place the disk in a read-only state.

CrystalDisklnfo gives as threshold the number of 10 as the danger point for your disk. I'm not sure that this number is the same as ADATA would specify for this disk, but your count of 72 is nowhere near it.

All the other attributes are excellent, with absolutely no errors recorded.

It's good practice to continue periodically checking your disks and their SMART data, to anticipate future errors.

  • 2
    I read "Counts the number of bad blocks. Raw Value Byte [3~0]: Early bad block count Raw Value Byte [5~4]: Later bad block count" for attribute 170? Could it have been changed in the document? Nov 24 at 1:32
  • @JoepvanSteen I read the same. But the real point is that all vendors have their own ways to use the attributes, particularly if we spek about raw values. And sometimes it is even not consistent between product lines. This attribute list clearly shows the attribute AA has not the same meaning depending on the vendor: data-medics.com/forum/threads/… . What is AA fo ADATA, we don't know for sure. If it is Kingston like, then this raw value shows 257 early bad blocks.
    – PierU
    Nov 24 at 6:51
  • 72 is the percentage remaining, probably. Raw value: 257.
    – user253751
    Nov 24 at 12:25
  • 1
    @PierU, True. Interesting link. Nov 24 at 13:41
  1. What is this bad block count and is it early or later bad blocks?

As others suggested I suspect early indicates bad blocks detected while the SSD was configured at factory. Which is weird and not common practice in the past where manufacturers tended to hide such defects.

  1. Are they excluded from I/O after being reported?


  1. Sometimes when copying a single large file, the speed drops to just 2 – 3 MB/s for a few seconds and then again jumps to 200 MB/s. Is this because of bad blocks?

I'd take a look at bad block count immediately after such an event. If number happens to increase after such an observed slow down, then yes it may very well be related. SMART values gain meaning if you can link them to such a specific event IMO.


What is normal and actually highly recommended is that your SSD has "spare" blocks that can be used at some point if some blocks on your SSD go bad. Your software may have an unfortunate choice of name for these spare blocks.

What is normal is that a brand new SSD is already using some of these "spare" blocks. Producing an SSD with 100% good blocks may be very expensive compared to one with 99.99% good blocks, and it's you who would pay the price difference.

What is also normal is that during operation some blocks turn bad and are automatically and invisibly for the user replaced with spare blocks.

What is bad is when your SSD has so many bad blocks that it runs out of spares to replace them.

  1. difficult to say if it's "early", "later", or "both", without the attribute description by the vendor (note: they all use the attributes in their own way, even the ones that are supposed to be standardized)
  2. obviously, yes
  3. normally they are, that's the point of flagging them as "bad"
  4. unlikely
  5. so far so good...
  6. maybe yes, maybe no. You should monitor the SMART report from time to time: if the bad blocks count stays stable then there's no need to worry; if it increases then the drive is dying.

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