Guest Janetb Posted July 18, 2007 Posted July 18, 2007 At Device Manager>Disk Drives>[R-click on particular disk drive]>Policies Tab, we can choose between Optimize-for-Quick-Removal or Optimize-for-Performance. I would normally use the Safely Remove Hardware Icon, so, on the on hand, I might as well take advantage of the Optimize for Performance option. But suppose a drive NOT optimized for quick removal inadvertantly becomes unplugged, or if there is a power blackout---what bad things can happen? Can I be in danger of losing all the data on the drive? And how much of performance improvement does the Optimize for Performance option afford? Not clear on the disadvantages (possible consequences) of each of the two options. I don't know what write caching is. Many thanks for input...! Janet
Guest M.I.5¾ Posted July 18, 2007 Posted July 18, 2007 Re: Write Caching vs. Safe Removal "Janetb" <Janetb@discussions.microsoft.com> wrote in message news:ADC4C801-F561-43C2-9C75-22EFB5A7C088@microsoft.com... > At Device Manager>Disk Drives>[R-click on particular disk drive]>Policies > Tab, we can choose between Optimize-for-Quick-Removal or > Optimize-for-Performance. I would normally use the Safely Remove Hardware > Icon, so, on the on hand, I might as well take advantage of the Optimize > for > Performance option. But suppose a drive NOT optimized for quick removal > inadvertantly becomes unplugged, or if there is a power blackout---what > bad > things can happen? Can I be in danger of losing all the data on the drive? > And how much of performance improvement does the Optimize for Performance > option afford? Not clear on the disadvantages (possible consequences) of > each > of the two options. I don't know what write caching is. > Drive cacheing come is two flavours. Write Back ('optimised for speed'): In this scheme, when you access a drive, the contents of the block (or blocks) that you are reading is copied into a faster memory system (usually RAM). This means that although the initial read is limited by the drive's speed limitations, subsequent reads from the same block are much faster. Most modern cacheing systems are able to 'que up' the next block in anticipation of reading. When it becomes necessary to perform a write to the drive, the write is instead written to the cached image in RAM and flgged as 'modified'. It is not actually written back to the drive until the processor is less busy (though there is usually (but not always) a maximum holding time beyond which a 'cache flush' is performed. The option should exist to force a cache flush (In Windows: the 'safely remove hardware' icon in the system tray). Write Through ('optimised for quick removal'): In this scheme the read cacheing works exactly like the previous case. However, when a write is performed, the write takes place directly to the drive medium avoiding the cache. The cache is flagged as being 'dirty' so that any future read of the cache must first perform a cache update (in many schemes, the write takes place to both the disk and the cache, but this makes little practical difference as far as the user is concerned). It should be clear that the first option provides for the fastest performance of the drive system ('optimised for speed'). However, the big disadvantage is if the drive is removed (or if the system power fails) before the cache flush takes place. In this instance, the data in the cache is lost and the drive will simply hold the previous version of the file. A more serious situation occurs if the drive is removed or the power fails *while* the cache flush is actually taking place. The upshot of this depends on at exactly what stage the write back had reached. The effect can vary from a corrupted file to a corrupted disk. The second option provides that once the write has taken place, the drive has the up-to-date data on it and can thus be removed almost immediately ('optimised for quick removal'). Which option you chose for your removable media depends on how disciplined you are at flushing the cache, and how likely you are to have a power cut at the wrong moment. For most users, I would recommend the the 'optimised for quick removal' option to avoid potential catastrophies (particularly users who are not savvy enough to understand cacheing). But if you believe that you have the necessary discipline; want the last ounce of speed and have a reliable power supply (or a UPS) then go for 'optimised for speed'. HTH.
Guest dobey Posted July 18, 2007 Posted July 18, 2007 Re: Write Caching vs. Safe Removal "Janetb" <Janetb@discussions.microsoft.com> wrote in message news:ADC4C801-F561-43C2-9C75-22EFB5A7C088@microsoft.com... > At Device Manager>Disk Drives>[R-click on particular disk drive]>Policies > Tab, we can choose between Optimize-for-Quick-Removal or > Optimize-for-Performance. I would normally use the Safely Remove Hardware > Icon, so, on the on hand, I might as well take advantage of the Optimize > for > Performance option. But suppose a drive NOT optimized for quick removal > inadvertantly becomes unplugged, or if there is a power blackout---what > bad > things can happen? Can I be in danger of losing all the data on the drive? > And how much of performance improvement does the Optimize for Performance > option afford? Not clear on the disadvantages (possible consequences) of > each > of the two options. I don't know what write caching is. > > Many thanks for input...! > Janet > Quick removal just means you can unplug without having to use the safely remove device icon. More useful for flash drives or small drives. I'm not sure but I expect this method copies each file from the disk then verifies it. This is slower to transfer as it has to read from source, write to destination, read from source, write to destination etc. Performance means faster transfer rates. Useful for external HDDs or large capacity storage when transferring large amounts of data in one go. Write caching is when a large chunk of data is stored in a cache, (not sure if this is the HDD cache, or a cache created in RAM, or from the pagefile), then written to the drive in one go. It is faster as it can use the maximum bandwidth for the transfer, but if the transfer fails all data in the cache will be lost. If you unplug anything, using any method while data is being transferred, (surprise, surprise!), the transfer will fail. If you aren't in a rush, and have no reason to believe your storage device won't fall of the desk and become unplugged, then no reason not to use performance. I expect most gains would be seen by using larger storage capacity such as external HDD enclosures. I haven't measured it myself, and it does depend on the chipset of your PC etc. You could run a test yourself by trying both methods and timing the transfer. Of course the flip side of that is, if you aren't in a rush you may as well use quick removal mode, as it doesn't really matter time wise if the transfer takes longer, so you can just unplug the drive when you are ready to leave. If you are using performance mode and unplug the device while it is not being used nothing bad will happen. I'm inclined to think MS goes overboard on the warnings sometimes, but then I meet users who do lots of stupid things then blame the OS/car/toaster for their ignorance. It may be possible to damage a mechanical drive, (spinning disk type devices), or mess up the file system if the device is powered by the USB port, but I think it is extremely unlikely it will be damaged by being unplugged during a transfer. As a general guide for flash drives, wait about 10 seconds for the file transfer window to disappear , maybe do a refresh of the drive to check the files exist on the device. It should be safe to unplug, regardless of method you have used. For external HDDs wait for the file transfer window to disappear and check to see that the "in use/activity" light on the external drive is off, then it should be safe to unplug or switch off.
Guest Zilbandy Posted July 18, 2007 Posted July 18, 2007 Re: Write Caching vs. Safe Removal On Wed, 18 Jul 2007 00:22:01 -0700, Janetb <Janetb@discussions.microsoft.com> wrote: >Not clear on the disadvantages (possible consequences) of each >of the two options. I don't know what write caching is. With write caching turned on, data may not get immediately written to the hard drive when you do a 'save' in some program. The data is kept in a queue and written to the drive when the system is less busy. Usually this won't cause any problems, but there is a chance of losing data. For instance, you are working on a Word document and you have a couple other things going on in the background. You save the Word document and 2 seconds later, the power goes out, the computer shuts off. With the write cache enabled, there is a possibility that the saved data has not yet been written to the hard disk, thus, you lose the data. With the write cache turned off, when you hit the save button, the data is saved immediately. If the little bar that indicates your filing being saved completes, the data is on the hard drive. On my desktop computers, I have write cache DISABLED. On my laptop, I have it ENABLED. The reason has to do with the time it takes for my laptop to go into 'hibernate (something my desktop doesn't need to do). With the write cache off, it takes several minutes for the laptop to hibernate. Why? I don't know. If the write cache is enabled, the laptop hibernates in 15 seconds. I'm sure someone at Microsoft could tell you why, but WinXP seems to need the write cache enabled if you wish to hibernate in a short time. -- Zilbandy
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