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btrfs Archives - AWS Managed Services by Anchor

The btrfs backup experiment

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Today we’re talking about our experience with btrfs, the next-gen Linux filesystem. btrfs has been maturing rapidly over the last few years and offers many compelling features for modern systems, so we’ve been putting it through its paces on some of our backup servers. How does it stack up? Read on! We chose to test btrfs on backup servers because they can make good use of the features on offer, and the threat-level of data loss is low. For our backups, the biggest benefit comes from copy-on-write and atomic snapshots. At Anchor we use a modified version of Dirvish with support for btrfs: instead of hardlinking directories to provide historical snapshots we just use btrfs’ snapshot facility, which is very quick. Expiring old snapshots is similarly quick – it’s a…

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How to explain Hash DoS to your parents by using cats

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We came across this interesting article recently, it’s about how an attacker can perform a denial-of-service attack by feeding perverse input to a system that uses weak hashing algorithms. This is referred to as a Hash DoS, and the specific target mentioned in the article is btrfs. btrfs is a next-gen filesystem that’s expected to replace ext3/4 in Linux. It’s still considered experimental but is quite usable and maturing fast. This article piqued our interest because we’re using btrfs “for reals” here at Anchor. It’s well and good to say that, but the article isn’t very exciting unless you have a background in computer science. How would you explain Hash DoS to your parents, who probably don’t have a CompSci background? This is the internet, so the answer is cats….

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100% FAT-free

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I wrote some documentation for our sysadmins last week detailing how one should deal with a critical diskspace notification at some ungodly hour of the morning. On the specifics of checking filesystems with the df tool: “Astute readers will notice that we don’t query btrfs filesystems here; this is because btrfs uses extents, and inodes are a non-issue.” Well, I wasn’t entirely wrong, but I wasn’t entirely right either. btrfs is a modern filesystem with lots of shiny new features. It’s definitely not production-ready yet, but like a magpie drawn to shiny things, a couple of us use btrfs on our own machines (it’s what backups are for, right?). Some time ago I wrote about how an ext filesystem can run out of free inodes and bite you. That happened…

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LCA day 2

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Bit of a quiet day today, the highlight was probably the presentations on btrfs and xfs. Btrfs has been developing nicely, and Avi Miller got up to spruik some of the newer features of the filesystem. A bit like ZFS (which isn’t compatible with Linux licensing terms), it pulls in a lot of smarts that are usually the domain of your RAID controller/subsystem. This means more flexibility in how you handle your data, but a lot of new complexity too. It’s exciting stuff, but we’ll be waiting a bit longer to consider it robust enough to use in production. We’d kill for the integrated snapshotting (great for backups) and data integrity checking (store CRCs with your data) features. Meanwhile, XFS reports steady progress and positions itself as the filesystem of…

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