Why a small SSD + large HDD?

This is related to the broken computer I mentioned previously that I'm
trying to fix for a friend...

The computer had a 2 TB drive that had failed. I think I've got that
under control (I'll post about that later.) It also has a 16 GB solid
state drive whose purpose is mysterious to me. As it turns out, the SSD
appears to be dead - it's not recognized by any computer I hook it up
to. I'm wondering if his computer took a power surge which corrupted
both the hard disk and SSD. Anyway, my questions are...

- What is the purpose of this small SSD? From what I read it probably
acts as a cache for the HDD. If so, what would happen if it failed?
Could that be responsible for the HDD corruption? Does it make a real
world performance difference? Is it worth replacing?

- If I replace it now do I just plug it in and the system (Win 8.1)
will figure out how to use it, or must I do some kind of setup?

Nil wrote:
This is related to the broken computer I mentioned previously that I'm
trying to fix for a friend...

The computer had a 2 TB drive that had failed. I think I've got that
under control (I'll post about that later.) It also has a 16 GB solid
state drive whose purpose is mysterious to me. As it turns out, the SSD
appears to be dead - it's not recognized by any computer I hook it up
to. I'm wondering if his computer took a power surge which corrupted
both the hard disk and SSD. Anyway, my questions are...

- What is the purpose of this small SSD? From what I read it probably
acts as a cache for the HDD. If so, what would happen if it failed?
Could that be responsible for the HDD corruption? Does it make a real
world performance difference? Is it worth replacing?

- If I replace it now do I just plug it in and the system (Win 8.1)
will figure out how to use it, or must I do some kind of setup?

"Could that be responsible for the HDD corruption?"

Absolutely.

While there is a procedure to flush the SSD back to
the HDD, that wouldn't happen under a failure scenario.

And SSDs have been known to "brick" just like that,
with no warning.

There are a few flavors of caching schemes. The
SSD device could be Robson.

https://en.wikipedia.org/wiki/Robson_flash_memory

You would need to review the hardware on the motherboard,
the chipset, Google on "cache" and the chipset name,
to start to narrow down which stupid scheme this one is :-)

Most people with a clue have concluded "if you need an SSD,
buy an SSD, don't fiddle with caches". Buy an SSD, do frequent
backups. Until you have a feeling for whether the generation
or instance of SSD you bought, is actually a winner.

While I might have fallen for this scheme a few years ago,
once you learn how the stuff works, you begin to see
potential holes in it. And usually, the people who have
this in their machine, don't even know it is there.
That's the really sad part. I don't mind a tech where
people are reminded regularly of the bailing wire and
binder twine used in what they bought. But my experience
is, a lot of this whizzy stuff, the owners don't
knot it is there, and they first learn about the
gruesome details, after a failure.

There was at least one of these schemes where you
could set it for "write-thru" or "write-back", and
one of those choices is a *lot* safer than the other.

Hybrid drives also use this concept, but they're usually
set up such that if the flash dies, the data is safe on
the HDD portion. When a caching technology is only used
to speed up reading (i.e. booting), that's not such
a bad thing.

Ot's almost as disappointing as discovering Windows was using
a RAM write cache on my new machine. I finally traced down
what factor influenced it, and whether Hotplug was enabled or
disabled, determined whether huge amounts of data would
be queued up in RAM (on write). That's not particularly
a "power-safe" idea. I first noticed that one day using
FFMPEG, and noticing a huge surge in thruput. And I was
asking myself "did the authors of FFMPEG build a
cache ? how clever". But it turned out it wasn't
FFMPEG after all. It was system wide. And I couldn't
believe that a software developer at Microsoft did that.

Paul

On Tue, 20 Dec 2016 18:44:54 -0500, Nil
wrote:

It also has a 16 GB solid
state drive whose purpose is mysterious to me.

How's it connected? Does it look like stand-alone marketing or are
you working in an altogether proprietary assembled computer? Reason
being, I've worked with MSI MBs, and a likes, sold after-market for a
third or quarter their counterpart when badged, that were special
production runs intended for DELL or HP system assemblies.

16G is really miniscule, hardly a SSD by most desktop standards. I'm
still running my first SSD, a regular SATA 64G Samsung, priced under
$50 near the time 128Gs models hit midstream. Sized alone, 64G would
be the entry or close to it for the inception of SSD for popular
builds.

Not saying, among a technological flotsam, there isn't some pretty
weird gear sold for SDDs at the bottom-end of a lowest-priced querry
on an Ebay search...no way --- and plenty of it, too, last I looked.

On 21/12/2016 7:44 AM, Nil wrote:
- What is the purpose of this small SSD? From what I read it probably
acts as a cache for the HDD. If so, what would happen if it failed?
Could that be responsible for the HDD corruption? Does it make a real
world performance difference? Is it worth replacing?

The OS usually needs about 50G of disk space.

On Wed, 21 Dec 2016, Mr. Man-wai Chang wrote:

On 21/12/2016 7:44 AM, Nil wrote:
- What is the purpose of this small SSD? From what I read it probably
acts as a cache for the HDD. If so, what would happen if it failed?
Could that be responsible for the HDD corruption? Does it make a real
world performance difference? Is it worth replacing?

The OS usually needs about 50G of disk space.


Really?

I'm using just under 8gig on this computer for the operating system, but I
think I stashed some photos in that partition.

The refurbished computer I'm about to move to, it has a bigger drive so I
allocated 15gigs for the OS, but that leaves lots of space.

But maybe that WIndows stuff is way more bloated. I wouldn't know.

Michael

On 21/12/2016 12:02 PM, Michael Black wrote:
I'm using just under 8gig on this computer for the operating system, but
I think I stashed some photos in that partition.

By "8gig", my guess is you were talking about the RAM or memory of the
PC, not disk storage.

The refurbished computer I'm about to move to, it has a bigger drive so
I allocated 15gigs for the OS, but that leaves lots of space.

But maybe that WIndows stuff is way more bloated. I wouldn't know.

Most Window$ OSes need about 40G of disk space to install. You might
wanna put the OS in the small SSD for fast start-up and program loading,
while putting your data in a bigger traditional, spinning hard disk.

I dunno the amount of data you got. If you didn't have much data, maybe
256G SSD could store both OS and data. But if you got loads of video and
songs, then a spinning terabyte hard disk is cheaper than SSDs.

It's always better to put OS and data into two separate partitions. This
way, you can always re-install the OS easily without affecting the data.
You might wanna learn a bit more on this using Google.

On 21/12/2016 7:44 AM, Nil wrote:
The computer had a 2 TB drive that had failed. I think I've got that
under control (I'll post about that later.) It also has a 16 GB solid
state drive whose purpose is mysterious to me. As it turns out, the SSD
appears to be dead - it's not recognized by any computer I hook it up
to. I'm wondering if his computer took a power surge which corrupted
both the hard disk and SSD. Anyway, my questions are...
....
- If I replace it now do I just plug it in and the system (Win 8.1)
will figure out how to use it, or must I do some kind of setup?

How did you control and confirm that the SSD was really dead?

Try replacing the SATA cables first. Also double-check the power cables
to the SSD was connected properly.

Use a Windows$ installation DVD/USB to boot up the PC. Check whether the
SSD was listed. Maybe it's just a corrupted partition table (the work of
a computer virus or malware?).

Michael Black wrote:
On Wed, 21 Dec 2016, Mr. Man-wai Chang wrote:

On 21/12/2016 7:44 AM, Nil wrote:
- What is the purpose of this small SSD? From what I read it probably
acts as a cache for the HDD. If so, what would happen if it failed?
Could that be responsible for the HDD corruption? Does it make a real
world performance difference? Is it worth replacing?

The OS usually needs about 50G of disk space.


Really?

I'm using just under 8gig on this computer for the operating system, but
I think I stashed some photos in that partition.

The refurbished computer I'm about to move to, it has a bigger drive so
I allocated 15gigs for the OS, but that leaves lots of space.

But maybe that WIndows stuff is way more bloated. I wouldn't know.

Michael


It depends to some extent, on the skill of the operator.

I usually turn off hibernation (which deletes hiberfil.sys)
and also reduce the size of the pagefile. So that's an example
of improvements you can make.

If I install a VM in VirtualBox, the .vhd file I use as a
container for Win10 might be around 11GB or so. But obviously
the OS is not going to be happy with zero slack. For one
thing, it would be constantly throwing up a "low disk warning".
And we wouldn't want that... You should have some slack space
for VSS shadow copies.

The smallest space usage comes from running Windows in
WIMBoot mode, which is similar to a Linux LiveCD with
persistent overlay. I don't have any figures for what
an "average" user has for storage requirements in that
case. The WIM file would be 3.5GB (and is compressed
with a good compressor). The thing is, every time a
security patch happens on WIMBoot, the equivalent of
squashFS is not updated, and the persistent overlay
grows with time. Just like I might run out of persistent
store on a LiveCD setup when I get near the 4GB limit
(which is caused by using FAT32). Microsoft decided
it would be clever to sell 32GB eMMC machines at the
$100 price point, and the user is expected to keep
the WIMBoot OS in there, as well as their data files.
So that tells you right away, that 50GB is not necessary.
And that a figure less than 32GB is possible.

And if you install Win10 in a too-small partition,
it automatically adjusts hiberfil or pagefile to
account for it. It's reasonably clever about
shoehorning.

And Windows isn't all that clever about cruft.
For example, if you uninstalled a package, there
might be an MSI still sitting on C: which could
reinstall the entire package. While I can spot
some of these things with WinDirStat or SequoiaView,
I don't know if there are any clever cleanmgr.exe options
for cleanup. Linux has some package manager commands
for housecleaning, for which there might not be
a direct Windows equivalent.

Paul