Will read speeds be increased with Raid 1 in FreeNAS?

[Nerevarine]

It must be theoretically possible to have just as high read speeds in raid 1 as in raid 0 with two drives, since the data COULD be read from two physical drives at the same time, if the file system allowed for this "double reading" in some way? And if it had a way to read it so it "stitched" together half of the data from each drive for any given file, even though all of the file would be on both drives.

Write speeds however would always be as slow as the single slowest drive ofc. Different thing.

Does it work like this in practice? Sometimes, always, never, why, why not?

 

[jgreco]

FreeNAS doesn't support RAID 1, or RAID 5, or other RAID levels. FreeNAS uses ZFS. Please see the new user presentation.

 

[Nerevarine]

FreeNAS doesn't support RAID 1, or RAID 5, or other RAID levels. FreeNAS uses ZFS. Please see the new user presentation.

Sorry for the confusion, but zfs has some corresponding (not identical though) modes right? Mirrored vdev's or something is what I read to be similar to raid 1 in that aspect, but I can't find exactly how it works and how it affects read speeds on a 2 drive pool compared to a single drive. Can someone please show me what I should looks at to find this, or explain it to me?

 

[INCSlayer]

Sorry for the confusion, but zfs has some corresponding (not identical though) modes right? Mirrored vdev's or something is what I read to be similar to raid 1 in that aspect, but I can't find exactly how it works and how it affects read speeds on a 2 drive pool compared to a single drive. Can someone please show me what I should looks at to find this, or explain it to me?

your post literally has a quote in it that says you should read the New user presentation

Sent from my Nexus 5 using Tapatalk

 

[Bidule0hm]

Please look at the links in my signature, especially the one about the terminology and the one about Cyberjock's guide ;)

 

[jgreco]

Sorry for the confusion, but zfs has some corresponding (not identical though) modes right? Mirrored vdev's or something is what I read to be similar to raid 1 in that aspect, but I can't find exactly how it works and how it affects read speeds on a 2 drive pool compared to a single drive. Can someone please show me what I should looks at to find this, or explain it to me?

A mirror vdev is ZFS's closest construct to something from the RAID world; a mirror vdev involves multiple copies of a disk. People often take this to mean "two" but in practice it often means "three" where valuable data is in play, since the failure of one half of a two-way mirror means that redundancy is compromised and further errors could wipe out data. It is possible to run wider if needed, though in such cases L2ARC may be a better choice.

In the OpenZFS implementation, one of several things may happen. If the vdev isn't busy, it is possible that ZFS will choose to have several physical devices seek and participate in the read, increasing overall read speed from the devices. If the vdev is busy, it is likely that only a single device will seek and perform the entire read, which increases parallelism in the system (meaning two or three things can be getting accessed literally simultaneously).

http://open-zfs.org/wiki/Features#Improve_N-way_mirror_read_performance
https://svnweb.freebsd.org/base?view=revision&revision=256956

It's important that we use the proper terminology when discussing ZFS, because using the wrong terminology quickly leads to confusion.

 

[Nerevarine]

A mirror vdev is ZFS's closest construct to something from the RAID world; a mirror vdev involves multiple copies of a disk. People often take this to mean "two" but in practice it often means "three" where valuable data is in play, since the failure of one half of a two-way mirror means that redundancy is compromised and further errors could wipe out data. It is possible to run wider if needed, though in such cases L2ARC may be a better choice.

In the OpenZFS implementation, one of several things may happen. If the vdev isn't busy, it is possible that ZFS will choose to have several physical devices seek and participate in the read, increasing overall read speed from the devices. If the vdev is busy, it is likely that only a single device will seek and perform the entire read, which increases parallelism in the system (meaning two or three things can be getting accessed literally simultaneously).

http://open-zfs.org/wiki/Features#Improve_N-way_mirror_read_performance
https://svnweb.freebsd.org/base?view=revision&revision=256956

It's important that we use the proper terminology when discussing ZFS, because using the wrong terminology quickly leads to confusion.

Thank you very much for this answer! Sorry I missed the signature stuff above people, stupid tapatalk wont show them.

I have one follow up noob question before I decide how to do this, I have a single striped drive currently in a pool of its own, the first drive installed in the NAS with jails and such on it (although no jails are running), and I want to mirror this with a second drive now. The data currently on the drive is replaceable, but I would like to mirror with the second drive without having to unload all the data on the first drive to a backup. I understand there is always some risk when not backing up first, but it is generally doable right? The second drive will of course be wiped before I begin.

I saw a guide with some commands on how to mirror a new drive to an existing one and not wipe the old one. Any thoughts on this, so I don't do something incredibly stupid?

 

[jgreco]

Aside from "yes you can do it, be careful, have fun?" No.

 

[Nerevarine]

Aside from "yes you can do it, be careful, have fun?" No.

Thanks, that was all I needed to hear :)