4/12/2023 0 Comments Zfs vs openzfsWe can check sector alignment by running gpart list on one of the disks in the gpart list da1Įfimedia: HD(1,GPT,b1c0188e-b098-11ec-89c7-0800275344ce,0x80,0x400000) The layout and size of these reserved sectors will depend on your operating system and partition scheme, but we'll use FreeBSD and GPT for this example because that is what's used by TrueNAS CORE and Enterprise. Next, we want to account for reserved sectors at the start of the disk. Other distributions may create a large or smaller swap partition or might not create one at all.ġ8 * 1000^4 - 2 * 1024^3 = 17997852516352 bytes By default, TrueNAS CORE creates a 2GiB swap partition on every disk in the data pool. If a running process needs more memory than is currently available, the system can unload some of its in-memory data onto the swap space. The swap partition acts as an extension of the system's physical memory pool. Starting with the capacity of the individual drives, we'll subtract the size of the swap partition. It will generally be easier for us to work in bytes so we don't have to worry about conversion between TB and TiB. We'll use 14x 18TB drives in two 7-wide RAIDZ2 (7wZ2) vdevs. Once we understand RAIDZ, understanding mirrored and striped vdevs will be simple. ![]() We'll start by picking a less-than-ideal RAIDZ vdev layout so we can see the impact of all the various forms of ZFS overhead. I've found that the best way to get my head wrapped around ZFS allocation overhead is to step through an example. There are layers of overhead that need to be understood and accounted for to get a reasonably accurate estimate. ![]() Because its on-disk structure is so complex, predicting how much usable capacity you'll get from a set of hard disks given a vdev layout is surprisingly difficult. This complexity is driven by the wide array of data protection features ZFS offers. Its on-disk structure is far more complex than that of a normal RAID implementation.
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