Drive Configuration Poll



  • Since I have to re-set up my array anyway, I figured I would post this poll and see what ML would do.

    WWMLD?

    I originally wanted to set up three SSDs in a RAID5 setup. That was going to be the most cost effective way to go and give me the storage I needed. It ended up that I got three drives that were double the original capacity I wanted. Since two of these double capacity drives could meet my storage requirement, I decided to put two of them into a RAID1 and put the third one on the shelf in case one of the array members died.

    Well, I've been thinking about it, and talking with a few people offline. I'm thinking maybe it would be best to go back to the original idea of just putting all 3 of them into an array. I'd have way more storage than I need, but could also run VM backups to the array. (Obviously only for issues with the VM itself, not for disaster recovery if the array/server dies.)

    So if you were in this situation ... what would you do?

    1. Just use 2 in a RAID1 and store the third drive as a replacement
    2. Use all 3 in a a RAID5 array


  • I would think RAID1 would be pretty safe, unless you have some kind of write/delete occurrence on the RAID1, which would instantly get written to the other drive.

    So with that, is RAID5 better? I know the saying is SSD RAID5, unless you want/can/need to splurge for RAID10.



  • Three SSD drives in RAID5 shouldn't be an issue at all. SSDs eliminate some of the negatives of RAID5.



  • It's really more ....

    1. would you use the drive even though you don't need it, just in case you ever do
      or
    2. shelve it for the future

    Makes me sad thinking of it sitting there unused. But, it would make me happy if I ever needed it.


  • Banned

    @coliver said in Drive Configuration Poll:

    Three SSD drives in RAID5 shouldn't be an issue at all. SSDs eliminate some of the negatives of RAID5.

    Yep.. SSDs in a RAID 10 is a waste..



  • @BRRABill said in Drive Configuration Poll:

    It's really more ....

    1. would you use the drive even though you don't need it, just in case you ever do
      or
    2. shelve it for the future

    Makes me sad thinking of it sitting there unused. But, it would make me happy if I ever needed it.

    To bad you can't just return it and save the money.

    So with that not an option... I guess it really doesn't matter which option you pick... There aren't any appreciable downsides to RAID 5 SSD. So as long as you never go to the dark side and treat those backups you mention as real backups...



  • @Dashrender said

    So with that not an option... I guess it really doesn't matter which option you pick... There aren't any appreciable downsides to RAID 5 SSD. So as long as you never go to the dark side and treat those backups you mention as real backups...

    The only real "upside" I see in either scenario is having an exact spare sitting around in case on of these puppies goes dead.



  • There's also the option of using 3 drives in RAID 1. You get three time the read speed and two drives worth of failure.



  • I haven't seen data about performance of RAID 5 vs RAID 1 with SSD but the typical "read-modify-write" penalty you get with RAID 5 shouldn't hurt too much with SSD latency. For me, the question is as much about capacity as performance. If you use 2 SSDs in RAID 1, the capacity is half what you giet if you use all three in RAID 5. To show this, let's assume the drives are 1TB:

    • 3 drives, RAID 5 (2+1) = 2TB useable capacity. You also have the benefit of 3 SSDs involved in every read. There isn't a "spare" sitting around waiting for a failure" - you're using all 3 drives.

    • 2 drives, RAID 1 = 1TB useable capacity. If you can use RAID 10, you'd have the benefit of 2 SSDs in on every IO. You of course had the spare drive if there's a failure. However, the reliability of SSDs we've seen is that they are much better than HDD so you might never need this spare drive.

    So without really knowing anything about your workload, I'd lean toward RAID 5.



  • @HPEStorageGuy

    Thanks for the detailed writeup.

    After my issues last night with drives, I decided it's not worth having a drive on the shelf for all those years, and not even knowing if it works or not.

    I'm going to go with the 2TB RAID5 setup. And also throw some holy water on the server. Someplace it can't get into the server, of course!



  • RAID 5 doesn't give you benefit of 3 drives in read. If the file is large enough you might get three, but if it's small enough you'd only get one, where the actual data is.



    1. Three drives is not enough to justify RAID5, and if you've got a lot of drives, jump over to RAID6 if you're just going for a ton of space. Though if you can setup a bunch of RAID10s that'd be better. However, three drives, it's just better to use RAID1.


  • @tonyshowoff said in Drive Configuration Poll:

    1. Three drives is not enough to justify RAID5, and if you've got a lot of drives, jump over to RAID6 if you're just going for a ton of space. Though if you can setup a bunch of RAID10s that'd be better. However, three drives, it's just better to use RAID1.

    You did see that this is SSD drives, right? and that he only has 3 drive, so RAID 6 and 10 are completely out. His only options are JOBD, RAID 1 with two drives, RAID 1 with three drives or RAID 5, or RAID 0.



  • @Dashrender said

    You did see that this is SSD drives, right?

    Yeah, considering that, I"m not really concerned about the read or write performance.



  • @Dashrender said in Drive Configuration Poll:

    @tonyshowoff said in Drive Configuration Poll:

    1. Three drives is not enough to justify RAID5, and if you've got a lot of drives, jump over to RAID6 if you're just going for a ton of space. Though if you can setup a bunch of RAID10s that'd be better. However, three drives, it's just better to use RAID1.

    You did see that this is SSD drives, right? and that he only has 3 drive, so RAID 6 and 10 are completely out. His only options are JOBD, RAID 1 with two drives, RAID 1 with three drives or RAID 5, or RAID 0.

    Yes? That's why I said not enough drives, I saw that, and I suggested 1# out of the polling options and specifically said 3 drives: " Three drives is not enough to justify RAID5, and if you've got a lot of drives, jump over to RAID6" and this tells you that 1) I knew he only had three drives and 2) I saw that the second option was for RAID 5 and was explaining why that's not a good option.

    Then I talked about the ideal if you do have enough drives just for making it clear what sort of setup you would want if you went beyond three drives, this information is useful to others reading beyond the OP.

    I don't know where you're confused, I answer it in the first sentence. And what do SSD drives have to do with it? They fail too. I'm not even concerned with performance in this regard, with RAID1 and RAID5 you still can lose 1 disk, but if there's even bigger problems, recovering RAID1 is a lot easier than RAID5.


  • Service Provider

    @tonyshowoff said in Drive Configuration Poll:

    And what do SSD drives have to do with it?

    They don't carry the URE risk of Winchesters which is by a huge margin the primary failure mode of parity arrays.



  • I'm about 3 seconds away from moving back to paper with this array, so it might not even matter.


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