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I build a microserver to access my personal data and web services from my client machines. Since this is all the stuff I collected in the past 15-20 years, I'd like to keep it safe, so I'd like to use RAID this time. I have already checked that only 3.5" HDD-s have rational prices, so using 2.5" hdd or ssd is not an option. The motherboard supports RAID 0/1/5/10. I am currently selecting a case, but I am not sure whether it should have 3 or 4 drive bays for 3.5" hdd-s. The case I really like (Tt Core V21) has only 3 x 3.5" drive bays. The other case which is not that good if we are talking about cooling and air flow (BitFenix Phenom Micro-ATX) has 4 x 3.5" drive bays. What are the pros and cons using 3 or 4 disks if we are talking about RAID? (I guess it is something general, but if not, then I'd like to know it by each RAID version.)

Conclusions:

  1. I think 3 drives with RAID-5 is sufficient for my needs.
  2. I need a self-healing filesystem like ZFS or BTRFS (I chose the latter one), which can fix data degradation using RAID parity data. These filesytems can make incremental snapshots too, so they are great if you want a fast backup without halting the system. Using an event storage can do the same on application level, so that part does not really matter in my case.
  3. People here never heard that backup does not protect against bit rot, but a self-healing filesystem with RAID most of the time does. Probably they are too focused on their RAID is not a backup mantra to learn new things...
inf3rno
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  • https://serverfault.com/questions/339128/what-are-the-different-widely-used-raid-levels-and-when-should-i-consider-them/339214#339214 – quadruplebucky Jul 08 '17 at 01:49
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    Repeat after me: RAID is not backup. Again: RAID is not backup. – EEAA Jul 08 '17 at 03:22
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    @EEAA - Rarely Accessible If Disaster – TheCleaner Jul 08 '17 at 03:50
  • @EEAA "How many drives do I need for RAID?" vs "What are the different widely used RAID levels and when should I consider them?". Just curious, how did you read that a duplicate? – inf3rno Jul 08 '17 at 07:33
  • @EEAA Thanks for the "not a backup" idea, I read some answers about it, but how is it connected to my question? I already understand that RAID protects from hardware failure only, I did not claim anything else... – inf3rno Jul 08 '17 at 07:49
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    RAID5 should never be used for anything. This article is ten years old but the problems outlined in there just got worse due to bigger disks: http://www.zdnet.com/article/why-raid-5-stops-working-in-2009/ – Sven Jul 08 '17 at 08:08
  • @Sven Thanks for your input! I'll consider buying a RAID-6 card. – inf3rno Jul 08 '17 at 08:24
  • @inf3rno "Since this is all the stuff I collected in the past 15-20 years, I'd like to keep it safe, so I'd like to use RAID this time." <-- that's what good, tested backups are for, not RAID. – EEAA Jul 08 '17 at 10:07
  • @EEAA I did not say I won't use an external backup drive, but the data is far from static and I don't want to save it every day. This is not business a week can be lost if 2 drives fail simultaniously... – inf3rno Jul 08 '17 at 22:02
  • @Sven I had the assumption that RAID protects against bad sector caused data corruption, that's why I wanted it, but it appears to be untrue. http://forums.storagereview.com/index.php?/topic/32544-raid-5-with-bad-fixed-sectors/ If so my only option is ZFS. – inf3rno Jul 10 '17 at 02:19

1 Answers1

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Depends on what level RAID you want to do, and of course that depends on what you want to do with the RAID :)

Also don't forget that with Linux you can do software raid, no hardware support needed. What is nice about this is that the raid drives can be moved to another machine and be brought back up quick and easy.

Minimum of 2 drives for both RAID-0 and RAID-1. Minimum of 3 for RAID-5, 4 for RAID-10. Of course, you can always add more... if that is of interest, you may want to look into LVM and RAID+LVM....

RAID-0 stripes the data across both disks, which can help speed things up for doing work like video capture. Since both disks are evenly used for data, if you loose a disk the -0 in the name tells you how much data you'll be able to get back.

RAID-1 mirrors the disk, keeping the 2 drives in synch. If you have a failure of one disk, you can recover. If you have a hot spare defined (a 3rd disk) you may not even notice when it fails.

RAID-5 writes pairs of bits of data across 2 disks and writes a parity bit of the 2 bits it just wrote to a 3rd disk. And of course it shuffles which disk gets which bit. Loose one disk, you can recover. Again, if you have a hot spare defined (4th disk) you may not even notice.

RAID-10 is really RAID-1+0. Start by setting up 2 identical RAID-1 systems (4 drives), and then make a RAID-0 volume out of them. As long as one drive in each RAID-1 array is good, you can recover from a failure, and you get the speed boost of RAID-0. For seamless fail over you'll need a spare drive for each RAID-1 set up (2 more drives, 6 total).

ivanivan
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  • Thanks! I am not sure what information is required to choose. The operating system and applications will run on an SSD. I am not sure about the databases yet, maybe the SSD will be enough for them. There are many file in the GB range too, so I'll need to storage those and probably back the databases to the RAID. So the most optimistic scenario that I store only files on the RAID and read speeds are important (1 Gbps), writes will be more or less rare. – inf3rno Jul 08 '17 at 01:33
  • I guess we are talking about RAID-5 or RAID-10. The RAID-5 with 4 drives appears to be better if we are talking about data losing probabilities. – inf3rno Jul 08 '17 at 01:37
  • Canonical question: https://serverfault.com/questions/339128/what-are-the-different-widely-used-raid-levels-and-when-should-i-consider-them/339214#339214 – quadruplebucky Jul 08 '17 at 01:49