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Windows 7: Show Us Your WEI


08 Jul 2009   #1131

 

A little history, courtesy of TechNet. To help you wrap your head around it, Snakefoot has this to say. Ubernerds, anyone? The more things change, the more they stay the same.

Failed writes of cached writes is indeed a cause of corrupted or lost data.


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08 Jul 2009   #1132

Windows 7 Ultimate 64-bit RTM
 
 

Quote   Quote: Originally Posted by Antman View Post
Failed writes of cached writes is indeed a cause of corrupted or lost data.
Thanks for including this link: Write Back Cache Experiments

That was a nice read and very informative. But VERY dated being written/done in 2003. In the 90s and even up to early 21st century, write-back caching was frowned upon because the controller chip technology wasn't nearly as advanced as it is today. Also, they're using EXT3 and other Linux file allocation methods and older ATA (IDE) drives, not NTFS or anything on the Windows side with newer SATA drives.

Let's not confuse write-back caching with disabling the write buffer flushing which is what that "advanced" mode or last checkmark box in Windows 7 is about. The two are a little different.

Yes, it is possible to lose and corrupt data with write-back caching enabled, but it's also possible to lose and corrupt data if your HDD or SSD is writing when it loses power, regardless of its cache state or operational mode. There is hardly any additional risk in using write-back caching these days (it is nominal).

In fact, for larger files, write-back caching will speed up writing and reading to/from a disk, lessening the risk. In smaller files, the overhead for working with the buffer is greater, and therefore it takes roughly the same time. With lots of reads and writes being queued up in the buffer (ie: when an application is loading and a log is being written), then having write-back caching is a little more risk.

Write-back itself means the data is flagged as being written to the drive even if it's still in the cache. But the cache is often flushed regularly and very quickly when the read/write demmand on the drive or drive array is low. There is actually a lower risk of data corruption (file partially written before a power loss or crash) with write-back caching because the write from a buffer occurs faster than a write-through transaction. But there is a higher risk of data loss (losing a files completely due to a power loss or crash).

If we Google it, you'll find advocates for both enabling it and disabling it. I only enable it when I'm gaming (reading files more than writing them) and disable it when I'm doing any real work. But regardless, the risk of data corruption and loss is there regardless of whether you enable it or not.

Either way, I always run on a UPS, but an O/S can still crash hard and lose data.
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08 Jul 2009   #1133

Windows 7 Professional, Windows Longhorn 4074
 
 

Quote   Quote: Originally Posted by ciphernemo View Post
O/S can still crash hard and lose data.
Tell me about it
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08 Jul 2009   #1134
DJG

 

Quote   Quote: Originally Posted by ciphernemo View Post
Write-back caching doesn't necessarily cause loss of data. It's different that the write buffer clearing options in the device manager.
Indeed - it just makes you more succeptible, how much more depends on your hardware & configuration. Pressing the reset button during write operations can also frappe your filesystem good, but not necessarily .

Edit: too much coffee ...
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08 Jul 2009   #1135

Windows 7 Ultimate 64-bit RTM
 
 

Quote   Quote: Originally Posted by DJG View Post
Indeed - it just makes you more succeptible, how much more depends on your hardware & configuration. Pressing the reset button during write operations can also frappe your filesystem good, but not necessarily .
Yup, very true.

Quote   Quote: Originally Posted by DJG View Post
Edit: too much coffee ...
Totally NOT TRUE!!! Wei canz neber hab too mutz coffeeeeee! *is a coffee addict*
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09 Jul 2009   #1136
DJG

 

Quote   Quote: Originally Posted by ciphernemo View Post
Yup, very true.



Totally NOT TRUE!!! Wei canz neber hab too mutz coffeeeeee! *is a coffee addict*
No, not addict, the proper term is "professional coffee consumer"
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09 Jul 2009   #1137

Windows 7 Ultimate x64
 
 

mine


Attached Thumbnails
Show Us Your WEI-my-wei.jpg  
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09 Jul 2009   #1138

Windows 7 Ultimate 64-bit RTM
 
 

Quote   Quote: Originally Posted by DJG View Post
No, not addict, the proper term is "professional coffee consumer"
Oh. I have to remember to use that term!
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09 Jul 2009   #1139

 

Quote   Quote: Originally Posted by ciphernemo View Post
...That was a nice read and very informative...
As was your post. In fact, of all the isolated banter in these threads, this is my favorite. Not because of it's subject matter, but because of it's form and content. If only we were all sitting about the conference room and learning together.
Quote   Quote: Originally Posted by ciphernemo View Post
...But VERY dated being written/done in 2003...
There is little if anything outdated in computer science. Babbage's work in mechanical computing will soon come full circle. See Kruglick, E.J.J.: Microrelay design, performance, and systems
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09 Jul 2009   #1140

Windows 7 Ultimate 64-bit RTM
 
 

Quote   Quote: Originally Posted by Antman View Post
There is little if anything outdated in computer science. Babbage's work in mechanical computing will soon come full circle. See Kruglick, E.J.J.: Microrelay design, performance, and systems
There is quite a bit of truth in that statement. Principles remain the same even if their application evolves. And even future technology is based on past principles: things are still governed by them same set of physics (even if we don't know the full extent of this 'set' yet).

What we're discussing here is a principle that hasn't changed.

What I mean by outdated is that it has evolved to the point of exponentially diminishing risk. Unfortunately, that risk never reaches zero, so yes, the principles are still the same. At least they'll be the same until the next technological architecture level, and even that may or may not eliminate risk of some caching methods.

For SSDs, I envision a controller and memory (buffer) chip that can keep itself powered long enough to flush its own cache in the event of power loss.
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