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ZFS Administration, Part XIII- Sending and Receiving Filesystems

Now that you're a pro at snapshots, we can move to one of the crown jewels of ZFS- the ability to send and receive full filesystems from one host to another. This is epic, and I am not aware of any other filesystem that can do this without the help of 3rd party tools, such […]

ZFS Administration, Part XII- Snapshots and Clones

Snapshots with ZFS are similar to snapshots with Linux LVM. A snapshot is a first class read-only filesystem. It is a mirrored copy of the state of the filesystem at the time you took the snapshot. Think of it like a digital photograph of the outside world. Even though the world is changing, you have […]

ZFS Administration, Part XI- Compression and Deduplication

Compression Compression is transparent with ZFS if you enable it. This means that every file you store in your pool can be compressed. From your point of view as an application, the file does not appear to be compressed, but appears to be stored uncompressed. In other words, if you run the "file" command on […]

ZFS Administration, Part X- Creating Filesystems

We now begin down the path that is the "bread and butter" of ZFS, known as "ZFS datasets", or filesystems. Previously, up to this point, we've been discussing how to manage our storage pools. But storage pools are not meant to store data directly. Instead, we should create filesystems that share the same storage system. […]

ZFS Administration, Part IX- Copy-on-write

Before we can get into the practical administration of ZFS datasets, we need to understand exactly how ZFS is storing our data. So, this post will be theoretical, and cover a couple concepts that you will want to understand. Namely the the Merkle tree and copy-on-write. I'll try and keep it at a higher level […]

ZFS Administration, Part VIII- Zpool Best Practices and Caveats

We now reach the end of ZFS storage pool administration, as this is the last post in that subtopic. After this, we move on to a few theoretical topics about ZFS that will lay the groundwork for ZFS Datasets. Our previous post covered the properties of a zpool. Without any ado, let's jump right into […]

ZFS Administration, Part VII- Zpool Properties

Continuing from our last post on scrubbing and resilvering data in zpools, we move on to changing properties in the zpool. Motivation With ext4, and many filesystems in GNU/Linux, we have a way for tuning various flags in the filesystem. Things like setting labels, default mount options, and other tunables. With ZFS, it's no different, […]

ZFS Administration, Part VI- Scrub and Resilver

Standard Validation In GNU/Linux, we have a number of filesystem checking utilities for verifying data integrity on the disk. This is done through the "fsck" utility. However, it has a couple major drawbacks. First, you must fsck the disk offline if you are intending on fixing data errors. This means downtime. So, you must use […]

ZFS Administration, Part V- Exporting and Importing zpools

Our previous post finished our discussion about VDEVs by going into great detail about the ZFS ARC. Here, we'll continue our discussion about ZFS storage pools, how to migrate them across systems by exporting and importing the pools, recovering from destroyed pools, and how to upgrade your storage pool to the latest version. Motivation As […]

ZFS Administration, Part IV- The Adjustable Replacement Cache

Our continuation in the ZFS Administration series continues with another zpool VDEV call the Adjustable Replacement Cache, or ARC for short. Our previous post discussed the ZFS Intent Log, or ZIL and the Separate Intent Logging Device, or SLOG. Traditional Caches Caching mechanisms on Linux and other operating systems use what is called a Least […]

ZFS Administration, Part III- The ZFS Intent Log

The previous post about using ZFS with GNU/Linux concerned covering the three RAIDZ virtual devices (VDEVs). This post will cover another VDEV- the ZFS Intent Log, or the ZIL. Terminology Before we can begin, we need to get a few terms out of the way that seem to be confusing people on forums, blog posts, […]

ZFS Administration, Part II- RAIDZ

The previous post introduced readers to the concept of VDEVs with ZFS. This post continues the topic discusing the RAIDZ VDEVs in great detail. Standards Parity RAID To understand RAIDZ, you first need to understand parity-based RAID levels, such as RAID-5 and RAID-6. Let's discuss the standard RAID-5 layout. You need a minimum of 3 […]

ZFS Administration, Part I- VDEVs

So, I've blogged a few times randomly about getting ZFS on GNU/Linux, and it's been a hit. I've had plenty of requests for blogging more. So, this will be the first in a long series of posts about how you can administer your ZFS filesystems and pools. You should start first by reading how to […]

How A ZIL Improves Disk Latencies

I just setup an SSD ZFS Intent Log, and the performance improvements have been massive. So much so, I need to blog about it. But first, I need to give you some background. I'm running a 2-node KVM hypervisor cluster replicating the VM images over GlusterFS (eventually over RDMA on a DDR InfiniBand link). One […]

How Much Swap?

I've been in the UNIX and GNU/Linux world since 1999. Back then, hard drives were barely passing double digits in GB, and RAM was PC100 speed at roughly 128 MB max. In fact, it wasn't uncommon for most systems to have 32 MB of RAM with an 8 GB hard drive. And we ran GNOME, […]

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