Raid

[McTechSolutions]

Hi Guys.

I am in the process of getting my system off the ground and just looking for a little guidance on Raidz. I come from a traditional background of RAID levels , 0 , 1 , 5 ,10 etc and know the pros and cons of each type.

I am reading on ZFS and Raidz etc but what i am looking for is some kind of Raid1 = RAIDz? , RAID5 = RAIDz?

In my system that i am building i am installing the OS to a USB key. I then have 5 x 6TB SATA3 drives. Now typically i would have set these up in RAID5 so that i can survive a drive failure. What would be the RAIDz equivalent of this?

Thanks in advance guys. Just trying to learn and understand a little more.

 

[danb35]

https://www.ixsystems.com/community/resources/introduction-to-zfs.111/

 

[droeders]

There are lots of good resources on the forum, and I would suggest you read some of them before diving into FreeNAS/ZFS.

You should read this first:

https://www.ixsystems.com/community/resources/introduction-to-zfs.111/

And here's a long list of good resources:

https://www.ixsystems.com/community/resources/links-to-useful-threads.108/

 

[Redcoat]

https://en.wikipedia.org/wiki/Non-standard_RAID_levels

Search on these forums and Google is your friend.

 

[jgreco]

I am reading on ZFS and Raidz etc but what i am looking for is some kind of Raid1 = RAIDz? , RAID5 = RAIDz?

RAID1 is functionally the same thing as ZFS mirror vdevs.

People want to invent equivalences between RAIDZ and RAID5/6 but while the goals are similar (better space usage than mirrors), the technical implementation is NOT. RAIDZ1 has "single parity" protection (RAID5), RAIDZ2 "double" (RAID6), RAIDZ3 "triple" (RAID-got-nuthin').

The similarity basically ends there.

RAID5 works by having a parity block for each stripe (like RAID4) but rotating it amongst the component devices (unlike RAID4). You can compute where each parity block is on a RAID5 array.

ZFS doesn't do this at all. Instead, ZFS treats the pool as a bunch of space with the interesting characteristic that there's multiple devices.

Pull up this image in another window.

Now here comes the thing that might break your brain. ZFS writes variable length blocks. It protects the BLOCKS with parity.

For an eight sector sized block, see LBA 0-1, this seems similar to RAID5 (or better yet RAID4) and anyone who's worked with RAID4 will be screaming "BUT WHAT ABOUT THE HOT SPOT THIS MAKES!" -- it doesn't, because ZFS doesn't need to read the parity block prior to writing. The parity is a function of the block being written, not a function of the disk stripe. There is no XOR against "existing" on-disk blocks.

For a single sector sized block, see LBA 3 disks D and E. Writing a ZFS block that is the size of a single sector still requires parity protection. Unfortunately, that works out to be as much space as the data that's being protected.

RAIDZ uses a variable amount of space to store your data.

This has some significant implications on pool design. RAIDZ1 pools are fantastic at storing massive amounts of sequential data, with space efficiency similar to RAID5. RAIDZ1 is not good at protecting small blocks of random data.

If you're going "uhhhh... this raises a lot of questions" don't feel bad. The pros and cons you learned for conventional RAID levels are basically worth almost nothing here in ZFS-land. A whole different set of rules apply.

 

[McTechSolutions]

Thanks for the replies chaps. I am still learning this freenas stuff and trying to soak it all up. I did spin up very basic freenas to try some different setups.

 

[Tigersharke]

In my system that i am building i am installing the OS to a USB key. I then have 5 x 6TB SATA3 drives.

Prior (significantly older) versions of FreeNAS worked adequately with the boot drive as a USB stick but nowadays it is highly recommended to use some type of SSD instead. An SSD will have considerably better longevity than any USB stick/key. Standard HDD as boot device is fine also.

 

[blanchet]

If you lack of SATA port for the boot device, a SSD coupled with a USB-to-SATA3 adapter, is a very acceptable solution.

 

[McTechSolutions]

Thanks mate. Do you mean one of them USB SATA / SSD drive enclosures?

 

[blanchet]

Thanks mate. Do you mean one of them USB SATA / SSD drive enclosures?

Yes, it will work, but if you have an internal USB port, a raw USB-SATA adapter is more convenient to directly screw the SSD inside the server.

 

[McTechSolutions]

I see. Thanks mate. Will keep this is mind