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

[Hsu, Aaron (NBC Universal)]

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