computer components & hardware - Reallocated Sectors Count

Norm X wrote:
Hi,
I have a Microsoft SS software RAID with two hard drives. Now
CrystalDiskInfo says the raw count for Reallocated Sectors Count is 2 on one
HDD. I like to get some lead time so I can purchase a cheap 480 GB SSD on
eBay. How bad it is it? Should I wait for the count to increase before I
worry?

Thanks.

If you see 100 Reallocated on Monday and 200 Reallocated on Tuesday,
it's time to get your replacement on order. You will get a better idea,
once the percentage indicator drops from 100% to 99%. At that point,
you can work out "how many reallocated does 1% represent" and then
you know the total pool remaining. The drives I have experience with,
the raw count goes to 5000 or 5500 or so. I would expect a 10TB
drive (something I don't own), has a different count limit.

One of the tests I run, is an HDTune transfer rate test ("benchmark").
It could be that all the bad sectors are concentrated in one area.
I find this is typically in the OS area, but it isn't always
like that. The purpose of the transfer rate test, is to see
if the disk health actually affects normal usage.

When my OS drive became perceptibly slow, the reallocated was
actually still 0, but the bad blocks were all concentrated in
a 50GB width swath. And I replaced the drive right then and
there. I didn't need those reallocated blocks, to turn into
CRC errors (and data loss) to convince me. Reallocated counts
are "thresholded", so the majority of reallocated counts
are hidden from you. There could be a hundred thousand
reallocated blocks, and we'd never know (except to notice
the performance issue they cause). Reallocated are thresholded,
so that when a hard drive is new, people won't "cherry pick"
drives by returning a drive showing 2 reallocated blocks.
If everyone had the technical ability to detect "perfect
drives", the lineup at the return counter at the computer
store, would go around the corner. So instead, the disk
companies lie to us, for our own good.

Reallocated, as a trouble indicator, works best if the
reallocations are spread uniformly over the disk surface.
But disks don't always have that pattern. Some disks, it
looks like a "wear" pattern, not an "age" pattern.

So transfer rate testing is just as useful as staring at the
Reallocated indicator.

RAID can hide the problems, depending on type. A RAID 1
mirror, the first drive ready, gets to return its read
sector to the user. So the "healthy" drive can shield
the truth from the RAID operator, on reads. Maybe on
reads, the read data from the slow drive is never used.

If the RAID is a RAID 0 stripe, the pattern may be hard to
interpret (due to the stripe size, and due to which blocks
HDTune is actually reading at the time). I can't offer any
real hands-on advice with this, is I would not be caught
dead running RAID on a home system. I have around two dozen
hard drives, and all of them run simplex. As a result, all
have working SMART and don't rely on passthru. And they're
easy to analyze, when looking for troubles.

SSDs still aren't "cheap". You only need sufficient capacity,
to host a boot OS. Like, Windows 10 OS works a lot better
on an SSD, and ~60GB is sufficient to satisfy an application
like that. Older OSes like WinXP, they don't need the the SSD
performance to get by. The smallest HDD is probably 1TB,
because the platters now are that big, or a bit bigger. For
the money you'd put into a 480GB SSD, surely more HDD capacity
could be purchased.

And for performance, the M.2 drives are pretty fast. And just
recently, the marketing geniuses have decided to make 4 lane
or 2 lane drives, so that they could have some "shabby cheap"
M.2 to fill the pricing holes between 4 lane M.2 and the slower
SATA III SSDs. To run an M.2, if the motherboard doesn't have
M.2, you might need a PCIe adapter card for those. A company
in Canada sells an expensive adapter, at around $100 or so,
which holds *4* M.2 drives. Which might be a good option if
you have a low-end desktop with limited lanes to work with.
That card actually has a PCIe switch chip, to share bandwidth
and make the most of a bad situation. Some cheaper Chinese
adapters, they'll be a lot cheaper, but they'll be using
up a precious slot to house a single M.2.

Paul