How RAID Works

What is RAID and how does it work? Why would you use RAID and what are the benefits in terms of performance and reliability? Dave Explains mirroring, striping, JBOD, RAID levels, and ZFS.

Upcoming LIVESTREAM: Tentative for Sunday the 9th at 10AM PST, 1 PM EST.

ERRATA: RaidZ2 can accommodate 2 failures, RaidZ3 can accommodate 3. Whoops!

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[amonynous]

calling his storage unit lil nas is such a power move

[kevinshumaker]

The one thing I've learned from experience:
DO NOT USE ONLY DRIVES FROM A SINGLE BATCH / DATE CODE & MANUFACTURER.
Mix your drive manufacturers. Mix your date codes. We had a 500TB Server go south within days due to the drives being all from the same manufacturer and date code, and a lot of drives failed and cascade failed. They were under warranty, and we did have a good tape backup, but it took a LONG time to do the swap, mixing, and restoring, the whole time we were down (about 10 days, tape is SLOW).

[kevintrumbull]

The ZFS equivalents to raid are RAIDZ1 for RAID5 (Single parity), RAIDZ2 for RAID6 (Double parity), and RAIDZ3 for triple parity RAID. The number after "RAIDZ" is the number of drives (parity) that you can lose before you have data loss.

It's worth noting that ZFS contains a large number of advancements beyond what traditional RAID offers, such as data integrity guarantees, transactional operation (which keeps the write hole from corrupting your array), and more.

[meggrobi]

I do like Dave's "conversational" presentation, it's interesting yet not over the top. I also like the trip down memory lane as I relate to many of his anecdotes. The loss of two drives, in a large array, is a thing when you take into account mean time failure.

[muchosa]

When I worked for VzB, I learned unless you test a backup, consider it bad. We had clients that did weekly restores of their data to confirm if it was good.

[marcfruchtman]

The "Count" was absolutely glorious!

[LogicalNiko]

Back in the day I had to write a recovery mechanism for 720MB SCSI-2 drives from a large raid set whose hardware controller failed and was basically unobtanium. IIRC we built a linux box with a big JBOD, and then basically selecting offsets from dd images of each drive. Then reconstructing the partitions in the right order. I remember we ended up using box fans and steel desk filing folder organizers to hold each of the drives and give them a decent heat sink. IIRC it took something like 7-8 days in those days to process such "massive" drives 🤣

[ferna]

Watched the whole thing. I love the thorough way you explain everything. Even though I work as a technician, I have 0 experience with RAID machines, so this is always useful. Thank you ♥

[katbryce]

I don't know how this storinator thing works, but in FreeBSD (and Solaris), which have had zfs for a lot longer than Linux, RAID-Z1 is sort-of equivalent to RAID 5, RAID-Z2 is sort of equivalent to RAID-6, and RAID-Z3 can cope with three drive failures.

One important thing about zfs is that it should always have access to the raw drives. You should not create a zfs file system out of "drives" that are RAIDed using some other method.

One big advantage that zfs has over standard RAID is that it can deal with non-catastrophic disc failures - where the disk is apparently still working, but giving back wrong data. In standard RAID, you get a parity error and you know something is wrong, but because you don't know which drive has failed, you don't know what the right answer is. In zfs, you will have a much better chance of knowing which drive is reporting the incorrect data.

[LanceMcCarthy]

I just bought a 12 disk, 4U JBOD. It uses a USB 3.2, but is architecture allows for parallel access to each internal SATA interface. It arrives tomorrow, can't wait to load it up.

[michaelpezzulo]

Far better explanation of RAID then the Linkedin learning video course. Everybody's gotta love a man who knows what he is talking about.

[SB-KNIGHT]

This was perfect timing for this episode on RAID. I am currently working on updating my old antiquated RAID-0 Striped array which has been serving me well for the past decade, but, its time to update to something a bit more reliable. Despite that, I have been using the same disks in it for over a decade and have not once had any data loss or disk failures (dispite living on the edge LOL). Always kept the data mirrored to another disk using SyncToy. BTW, Who made that wonderful app and why did it never gain traction? Its a great utility and has always worked great for copying large amounts of data from one place to another with different modes and having a way to verify the operations. Keep up the great work Dave! This is now one of my new favorite channels. Cheers!

[TractorWrangler]

Your channel is great. Lots of information from behind the user perspective that is never seen by the end user. Love your content.

[ianjharris]

Dave you bring these subjects to practical reality from your experience. An obvious pro.

[homemedia]

@12:18 ... I was waiting to hear you say this... haha ... "RAID is not a backup" - I learned the hard way many years ago :D
Edit: I use Ceph via Proxmox... it is like raid spanned across 2 or more servers (3 is the recommended minimum) - however, I have backups to a RAID Mirror and important things go to the cloud! - great vid :)

[marksterling]

Loved this video, reminded me of my first production netware server, an eisa 486 with 2 scsi cards and 1gb scsi disks mirrored. The disks were full height 5 1/4 inch monsters. 2 years later I installed compaq proliant 1500s with the hot plug 2gb drives and the smart array raid5 with 4 active disks and a hot standby. At that office we ended up with 6 servers in that configuration. And with the 30 drives we would get at least 1 amber alarm on a disk every month or so.

[daishi]

Back in 1999-2000 I worked for a bank in London (city of) and was put in charge of the servers in the disaster recovery building across the river (south London) I don't remember how many servers and it it fluctuated all the time, but it was always full and took up 3.5 acres. I would constantly be coordinating with the main building for data recovery testing because although I had 3.5 acres of servers it was only a mirror of what was in the main building and it was also mirrored to Germany. One day the bank of England wanted to know what the data delay was between the main building and my site and due to this being unacceptable (if memory serves it was up to 45 mins by the end of the day) I was tasked to decide how this could be remedied. My options were take up almost all the copper cables across the river (they did not want it bounced off other sites/exchanges) or fiber optics for which I was told there was plenty that was still dark so I chose fiber. It turns out the a lot of the fiber was damaged so they still ended up digging up the roads to put in more fiber (apparently the Bank of England is a really good stick to hit telecoms companies and local governments with because it was started almost immediately) So anyone who was stuck in traffic near either London or Southwark Bridges in the later half of 2000 I'm sorry.
TLDR RAID across building/river is cool :-)

[skooby]

Thanks Dave. Informative and interesting. Love your work.

[itsyaboikirbo]

Thank you so much for explaining this! I look forward to more quality content from you! :)

[silentjohn]

I love ZFS, it has a lot of great features. And the zpool and zfs tools are very well documented. My config is 1 zpool with 2 raidz2-volumes of 6 disks each.