[Ham-Computers] RE: Flash Drives - Any Real Advantage to Write Caching?

[Jim Hill]

Thanks for the info, Aaron.
During my trip to Alaska this summer, I dropped my laptop.  I stopped 
by a computer store to see if it could be repaired.  It couldn't, but 
the tech managed to get all the data off the hard drive. I bought an 
external drive to store the data, and when I came home, I discovered 
it had a FAT32 partition instead of NTFS.  I wondered why.
Jim



At 11:11 AM 12/3/2007, you wrote:
>The only advantage of enabling write caching on a flash drive is a 
>quicker "return to OS" when you write to the drive.  In other words, 
>an application you're using will respond to a write command 
>"immediately" and you can continue to do whatever else you wanted to 
>do in that app.
>
>There are several potential disadvantages:
>
>* The system uses physical RAM to do the caching.  This takes away 
>from what the OS can use until the cache is completely flushed.  If 
>you're writing 1GB to the flash, Windows may allocate a large chunk 
>of memory from the "system pool" to cache the write.
>
>* Data corruption if the flash drive is pulled before the cache is 
>fully flushed (causing incomplete writes).
>
>* Although it may seem "faster", the data "write" to the flash is no 
>faster than before - it's just that you get control of the app/os 
>sooner.  With a modern multi-tasking OS (WinNT/2K/XP/Vista, 
>Linux/Unix, etc), return of control isn't as big an issue as before.
>
>
>My general recommendation is to disable write-caching on any 
>"removable" drive (flash, HD, Zip, whatever) - this is just good 
>general practice.  It's too easy to "unplug" such drives, esp if 
>you're in a hurry and forget to do the "Safely remove..." 
>process.  For most, remembering to use the "safely remove" function 
>is the #1 cause of removable drive problems. This is compounded if 
>write-caching is enabled.  Personally, I rarely use the "safely 
>remove" function, but I have write-caching disabled and I know what 
>to look for when it's safe to remove the drive.
>
>As to time savings, there is none - data can be written only as fast 
>as the drive will allow - enabling write-caching can't increase the 
>transfer rate to the drive.
>
>Last, the reason Windows won't allow you to "safely remove" a device 
>can be one of many things.  The most common is that there is a file 
>open on the drive - until this file is closed, you can't "safely" 
>remove the drive (and write-caching can't change this fact).  Also, 
>the preferred format for removable drives is FAT/FAT32 - NTFS can be 
>problematic on a removable drive unless you're careful (*ALWAYS* use 
>the "safely remove" function and make sure write-caching is *always* 
>disabled on a removable drive formatted with NTFS).
>
>Post another message (or PM me) if you need more details or info.
>
>
>73,
>
>   - Aaron Hsu, NN6O
>
>
>-----Original Message-----
>Sent: Sunday, December 02, 2007 7:41 PM
>Subject: [Ham-Computers] Flash Drives - Any Real Advantage to Write Caching?
>
>I understand using the "Safely Remove Hardware" icon on the system 
>tray allows write caching to be completed before the flash drive is 
>removed.  See http://www.pcguide.com/ref/hdd/op/cacheWrite-c.html 
>for a typical description.  Write caching can be enabled or disabled 
>by write clicking My computer, Selecting Properties, then the 
>Hardware tab in the properties window, then the Device Manager. In 
>the Device Manager window,  expand the Disk Drives icon by clicking 
>on the small + box.  Write click on the flash drive name, select 
>Properties, then the Policies tab.
>
>I use flash drives only to store data, and wonder if there is any 
>real time saving when  write caching is enabled.  Sometimes I'm not 
>allowed to safely remove hardware, and not using it would avoid this problem.
>
>Jim
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