![]() ![]() There isn’t much you can do to protect against forced restarts, other than ensuring that your Mac has a minimum of kernel panics. A kernel panic in the Mac, or loss of power to either Mac or backup drive, are well-known causes of errors in the backup. The most vulnerable time for your backups is when a backup is being made, as that’s when files and links are being written. Their frequency and severity have been reduced with the introduction of journalling to HFS+, but they do still occur, and appear most common in sparsebundles, if user reports are anything to go by. The commonest causes given for significant directory damage are forced restarts following kernel panics, and sudden loss of power. It’s perhaps unsurprising that, among those millions of directory entries, errors can occur, and their directories can become sub-optimal and slow to access. The file system directories on backup volumes thus grow over time to become huge, with the majority of their entries being hard links. Over a year of use, a busy Mac can readily accumulate more than 1 TB of backups, in millions of files and folders. ![]() The latter are essential to minimise the number of hard links to files, and a key feature of TM backups. Your backups don’t just contain copies of each file as it has changed over time, but a much greater number of hard links to previously saved files, and – a distinctive feature of HFS+ – hard links to directories. This is good because HFS+ is an old file system so has plenty of support in third-party utilities, and it’s bad because it isn’t particularly fault-tolerant. This article suggests what you can do to prevent such nasty shocks, and how you can ensure your backups will work when you want them to.įor the moment at least, all TM backups are made and maintained on HFS+ volumes, either running as the file system on a local disk, or in a ‘virtual’ HFS+ file system in a sparsebundle, in the case of shared or networked backups. Although this is the rule, there are also plenty of exceptions who go to their TM backup only to discover that it can’t restore a lot of what should have been there, or the whole backup is as broken as that failed disk. When that rickety old hard drive does fail, we expect to be able to replace it, restore from our backup, and carry on as before. Since TM, the majority of those submitting questions are regularly making backups, almost all of them using TM.Īs we’ve come to make backups, so we’ve come to rely on them. ![]() Before the introduction of TM, suggesting that the user went to their backups was like asking them to walk unaided to the South Pole. I’ve been writing Q&A and other technical sections for Mac magazines for over thirty years now, and can’t even guess how many letters and messages I have received asking what to do after hard disk failure. It’s easy to underestimate the importance of Time Machine (TM) to Mac users. ![]()
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