10.5: Improve networked Time Machine performance

May 13, '08 07:30:00AM

Contributed by: beba

After using a 500GB Time Capsule for Time Machine backups for awhile, I noticed increasing duration of the backups. Mainly the prepare and post-processing phases, and transfer of large number of small files, took a lot of time. For the transfer of large files, the slowdown was not so noticeable.

I inspected the sparsebundle disk image on the Time Capsule, and inside the disk image bundle of about 150GB, I found nearly 20,000 band files of 8MB each in a single folder. These 20,000 data pieces contain the data of the backup image. When Time Machine reads, creates or deletes folder structures in the backup image, the operating system must randomly access data distributed over these 20,000 band files. And that causes a remarkable amount of additional administrative accesses to the AppleShare volume of the Time Capsule.

I decided that a better size of the bands of the backup sparsebundle disk image is 1GB, i. e. my 150GB backup would contain about 150 band files in one folder. I converted the Time Machine backup image with the following method, which will also work fine for an AirPort-connected hard drive, not just for a Time Capsule.

[robg adds: Note that the following solution is clearly not Apple-approved, and there may be very good reasons why Apple chose an 8MB band size. If you're going to try this hint, realize that you're potentially endangering your backups. With that said, I've noticed the same performance issues on the USB-connected hard drive on my AirPort Base Station, so I'm going to try this later today to see how it goes. (I use this disk for backups of our laptops, neither of which contain critical can't-lose information, so it's a relatively low-risk test.) Read on for the proposed solution...]

Before you begin, note that this hint requires that the Time Machine disk has enough free space to hold another copy of the backup disk image.

Now notice that the Time Machine backups are (hopefully) running a little bit faster than before. When you are happy with the new backup disk image, later delete the OLD_MyMac_001acb9cb23d.sparsebundle image.

CAUTION: If anything goes wrong, you may destroy all of your Time Machine backups! And there is no guarantee that the converted backup disk image works fine in the future, i. e. when the Time Capsule fills up, or when Apple changes the Time Machine software. Apply this hint on your own risk.

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