Write cache is a facility where the OS stores data that should have been written to a drive, and then writes it later.. Without cache enabled: A normal program passes a write request to the OS to have data at a certain set of memory locations written to a drive - The OS then writes that data, gets a verification from the drive that it's been written correctly Then the program that asked for that data to be written is allowed to continue
With cache enabled: A normal program passes a write request to the OS to have data at a certain set of memory locations written to a drive - The OS then copies the data from those memory locations into it's write caching area and the program that asked for that data to be written is allowed to continue The benefit being that it's not held up waiting for the data to be passed to the drive, and the heads to be positioned, and the disk to spin round at least once (get to the place to be written, and then for that place to come around again to be read The problem - if the drive is too busy, or something else is using so much of the system that the data doesn't get written to the drive - then you've lost that data To 'manage' that possibility - the system reports a timeout if the data isn't written within a set time interval A retry will usually get the data written Then again - it may have been a USB/firewire, or other 'removable' medium - and if it's disconnected then tough luck hence the 'safely remove' thingy So - portable drive -probably better to have it disabled if you were getting problems (and you can probably guess the effect of not updating the allocation tables or root/master directory) The OS drive - normally you should have write cacheing enabled on that - or you can find the system gets very slow a 7200rpm drive takes about 8 milliseconds per revolution, so - that's 8 milliseconds every time anything is written to the drive, not even bothering to consider that a system that writes a block of a file every time it adds any data to the file would, with cache enabled - simply get the bit of data in cache changed - so no write cache and a log of 50 byte enries will have 10 writes performed for every 512 byte sector - an additional half a second delay for every sector of data in the written file You should, hopefully, be able to set write cache individually for each device allowing you to have the OS drive caching enabled, and the removable one disabled Then again, if both devices are both on the same controller the OS may be awkward about it JimB ----- Original Message ----- From: "Pranav Lal" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Saturday, September 16, 2006 9:32 PM Subject: Write chaching > Hi all, > > Should write caching be enabled or disabled? I have a portable hard drive > and I was getting some write caching errors so I disabled write caching for > that drive. Since then, I have been getting the following warning in the > system log > The driver disabled the write cache on device \Device\Harddisk0\DR0. > > The write caching for my primary hard disk is also disabled. Do I let things > be or do I enable write caching? > > Pranav > -- ---------------------------------------- To Change your email Address for this list, send the following message: CHANGE WIN-HOME your_old_address your_new_address to: [EMAIL PROTECTED] Note carefully that both old and new addresses are required.
