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Apple Computing Products:
macOS - Operating System
Time Machine - Backup Runs out of space
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<blockquote data-quote="MacInWin" data-source="post: 1850096" data-attributes="member: 396914"><p>The general rule of thumb is to have twice the space on the backup drive as the amount of data being backed up. So if your 500GB drive is, as you say, "quite full," then a 1TB backup drive should work. However, TM needs scratch space on the drive being backed up, so if you are "quite full" to the point of not leaving sufficient scratch space, backups will fail, no matter how much room is on the target drive. Even on SSD internal drives it's good to leave 5% or more free space for the system to use as scratch space.</p><p></p><p>Another factor is that the way TM works means that if you have a lot of really big files with high volatility (long videos being constantly revised, for example), then the thumbrule doesn't work so well. In that case you might need 4 or more times the space, depending on how far you want to go back.</p><p></p><p>Let me give some examples. Let's say your 500GB internal is at 490GB used. On first backup that 490GB is transferred to the backup drive as the base backup. Now an hour later any files that have changed are backed up, so let's say you were editing a 10GB file and have saved three histories in that hour, so that's 30GB, plus any other smaller files (Logs, plists, mail, texts, etc) that may have changed, so another 35-40GB is added to the backup. Now you continue editing that file for another 3 hours to get it right and each hour TM dutifully copies over 45GB to the backup. At the end of the day your backup will have 670GB used, approximately. Day two you decide to edit another video, this one 300GB. Your editor warns that you are out of space for history, but you press on, make the edit and let the history be lost. But the 300GB file has changed, so TM now copies that 300GB file, plus the other stuff, to the backup, so now you have about 975GB used on the backup drive in just two days. Pretty quickly you get to a situation where there is not sufficient space to make a new backup, but there are not enough backups on the drive for TM to do the juggling it needs to do to delete one of the backups in the middle, while preserving your history all the way back to the base backup for unchanged files and folders, so it throws up the error. How to fix it? Get a bigger drive, one sized to the way YOU work rather than the rule of thumb that works for most folks. </p><p></p><p>Think you don't use big files? Consider this: if you keep email going back years, that file and the database of attachments associated with it could well be gigabytes of storage, and every new message that comes in changes the file and the entire thing has to be backed up. Ditto for texts if you use Messages. Normally these are not large files, but they CAN get that way.</p><p></p><p>So what are you doing with your system that may make your backups larger than "normal?"</p></blockquote><p></p>
[QUOTE="MacInWin, post: 1850096, member: 396914"] The general rule of thumb is to have twice the space on the backup drive as the amount of data being backed up. So if your 500GB drive is, as you say, "quite full," then a 1TB backup drive should work. However, TM needs scratch space on the drive being backed up, so if you are "quite full" to the point of not leaving sufficient scratch space, backups will fail, no matter how much room is on the target drive. Even on SSD internal drives it's good to leave 5% or more free space for the system to use as scratch space. Another factor is that the way TM works means that if you have a lot of really big files with high volatility (long videos being constantly revised, for example), then the thumbrule doesn't work so well. In that case you might need 4 or more times the space, depending on how far you want to go back. Let me give some examples. Let's say your 500GB internal is at 490GB used. On first backup that 490GB is transferred to the backup drive as the base backup. Now an hour later any files that have changed are backed up, so let's say you were editing a 10GB file and have saved three histories in that hour, so that's 30GB, plus any other smaller files (Logs, plists, mail, texts, etc) that may have changed, so another 35-40GB is added to the backup. Now you continue editing that file for another 3 hours to get it right and each hour TM dutifully copies over 45GB to the backup. At the end of the day your backup will have 670GB used, approximately. Day two you decide to edit another video, this one 300GB. Your editor warns that you are out of space for history, but you press on, make the edit and let the history be lost. But the 300GB file has changed, so TM now copies that 300GB file, plus the other stuff, to the backup, so now you have about 975GB used on the backup drive in just two days. Pretty quickly you get to a situation where there is not sufficient space to make a new backup, but there are not enough backups on the drive for TM to do the juggling it needs to do to delete one of the backups in the middle, while preserving your history all the way back to the base backup for unchanged files and folders, so it throws up the error. How to fix it? Get a bigger drive, one sized to the way YOU work rather than the rule of thumb that works for most folks. Think you don't use big files? Consider this: if you keep email going back years, that file and the database of attachments associated with it could well be gigabytes of storage, and every new message that comes in changes the file and the entire thing has to be backed up. Ditto for texts if you use Messages. Normally these are not large files, but they CAN get that way. So what are you doing with your system that may make your backups larger than "normal?" [/QUOTE]
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Apple Computing Products:
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Time Machine - Backup Runs out of space
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