Those interested in the hairiest details are encouraged to check out this detailed comment in the original code commit. The logical layout is also randomly permuted to distribute things more evenly across the drives based on the offset.
Openzfs 2.1 full#
The full picture includes groups, slices, and rows that we won’t go into here. Please note that these charts simplified.
Openzfs 2.1 free#
The initial mistake leaves holes in most of the data groups (stripes in this simplified chart): 0īut when we silver again, we do this on the previously reserved free capacity: 0 Let’s take the simplified diagram above and examine what happens when one hard drive from the array fails. If a disk fails in a dRAID vdev, the parity and data sectors that lived on the dead disk are copied to the reserved spare sectors for each affected stripe. advertisingĭRAID adopts this concept – distributing the parity to all hard disks instead of bundling everything on one or two hard disks – and expands it spares. RAID5 dispensed with the hard disk drive with fixed parity and instead distributed the parity over all hard disks in the array – which enabled significantly faster random write operations than the conceptually simpler RAID3, since it did not interfere with every write operation to a hard disk with fixed parity. The first parity RAID topology was not RAID5 but RAID3, where the parity was on a fixed drive and not spread across the array. In fact, dRAID goes one step further with the concept of “diagonal parity” RAID. In a world of perfect vacuum cleaners, frictionless surfaces, and spherical chickens, a draid2:4:1 would look something like this: 0 We created a single dRAID vdev with 2 parity devices, 4 data devices and 1 replacement device per stripe – in compressed jargon, a draid2:4:1.Īlthough we have a total of eleven hard drives in the draid2:4:1, only six are used in each data strip – and one in each physically Stripes. In the example above we have eleven hard drives: wwn-0 by wwn-A. We can see this in action in the following example, which was taken from the documentation on the basic dRAID concepts: :~# zpool create mypool draid2:4d:1s:11c wwn-0 wwn-1 wwn-2. These numbers are independent of the number of actual hard drives in the vdev.
When creating a dRAID vdev, the administrator specifies a number of data, parity and hot spare sectors per stripe. Distributed RAID (dRAID) is a completely new vdev topology that we got to know for the first time in a presentation at the OpenZFS Dev Summit 2016. If you already thought that the ZFS topology was a complex topic, you will be surprised. Since then it has been tested intensively in several large OpenZFS development companies – which means that today’s version is “new” in production status, not “new” as untested. dRAID has been in active development since at least 2015 and reached beta status when it was merged into OpenZFS Master in November 2020. Today we’re going to focus on what is arguably the biggest feature OpenZFS 2.1.0 adds – the dRAID vdev topology. This release brings several general performance improvements, as well as some entirely new features, mostly aimed at enterprise and other extremely advanced use cases. The new version is compatible with FreeBSD 12.2-RELEASE and higher as well as the Linux kernels 3.10-5.13. 0 of our all-time favorite file system, “It’s complicated, but it’s worth it”.
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