SSD on Pro

mps wrote:
StephenB wrote: Also, I don't see a lot of value in using RAID with SSD. They don't have the same failure mechanisms as hard drives. Sizes also aren't aligned with hard drive sizes. I suspect your 512GB hard drives are actually 500 GB. Can you please elaborate on the problem with using SSDs in RAID? I'm using X-RAID2, which IIUC works with mixed-size drives and provides redundancy.

Assuming I am correct in thinking that your hard drive is 500 GB and your SSD is 512 GB, then you will probably have trouble simply inserting the SSD into the RAID array. With XRAID2, a new drive is either (a) >= the largest drive in the array or (b) exactly the same size as the drive it is replacing.

Also, I said I didn't see much value in SSD in RAID. A single SSD is faster than gigabit ethernet, so there is no performance gain in a RAID array of SSDs over jbod. With RAID-1 or RAID-5 you double the disk writes over jbod, with RAID-6 you triple the disk writes. And the writes to a consumer grade SSD are what limit its life. If all the SSDs are identical, and in the same array, then the writes should also nearly identical. So my guess is that they are even more likely to fail together than traditional drives, overwhelming RAID protection.

And with jbod, you can get trim to work more easily.

In your case, you are proposing a mix of SSD and hard drives. Your music files and directories will be partly on SSD and partly not. It won't be slower than your current setup, but it seems unlikely to be a giant step up either.

So if it were me, I'd back up the music, etc. and remove all the drives. Then install the two SSDs as jbod, load up some music, and see how it performs. If it works, then solve the trim problem, perhaps add in some the hard drives as a second RAID-1 volume and go from there. If it doesn't help, then power down, install all your old drives and you are back to where you are now.

Very interesting post, StephenB. Thinking out loud below.

StephenB wrote:
Assuming I am correct in thinking that your hard drive is 500 GB and your SSD is 512 GB, then you will probably have trouble simply inserting the SSD into the RAID array. With XRAID2, a new drive is either (a) >= the largest drive in the array or (b) exactly the same size as the drive it is replacing.

I didn't realize this. Looks like I'd have to replace them all at once. Not a dealbreaker, but definitely more painful.

Also, I said I didn't see much value in SSD in RAID. A single SSD is faster than gigabit ethernet, so there is no performance gain in a RAID array of SSDs over jbod.

I think there would be a big performance gain since LMS is running directly on the ReadyNAS and often does disk-intensive operations like scanning my music collection or Sqlite queries.

With RAID-1 or RAID-5 you double the disk writes over jbod, with RAID-6 you triple the disk writes. And the writes to a consumer grade SSD are what limit its life. If all the SSDs are identical, and in the same array, then the writes should also nearly identical. So my guess is that they are even more likely to fail together than traditional drives, overwhelming RAID protection.

That is an interesting observation. How would you provide redundancy then?

And with jbod, you can get trim to work more easily.

IIUC, the garbage collection on newer SSDs is good enough that TRIM is more of a "nice to have" than "have to have"

In your case, you are proposing a mix of SSD and hard drives. Your music files and directories will be partly on SSD and partly not. It won't be slower than your current setup, but it seems unlikely to be a giant step up either.

No. I am proposing a "pure SSD" solution.

So if it were me, I'd back up the music, etc. and remove all the drives. Then install the two SSDs as jbod, load up some music, and see how it performs. If it works, then solve the trim problem, perhaps add in some the hard drives as a second RAID-1 volume and go from there. If it doesn't help, then power down, install all your old drives and you are back to where you are now.

That approach is appealing, but I think it comes back to the question of how I'd provide redundancy in case of a disk failure. While I make occasional backups, RAID has proven invaluable to me for seamless real-time protection when a disk failed.

We agree that SSDs are faster than hard drives, and that you see the most gain on random read operations like database queries.

I haven't researched TRIM lately. It was added to Windows, and the only systems I have SSDs in today are Win 7, so I didn't worry about it. I've just assumed it is still needed...

RAID redundancy is great for keeping data available while you repair failures or expand your storage. Though given the relatively small size of SSDs, the restore time from backup isn't that long. I'd still go with jbod to get the most space from the SSDs and restore from backup when/if it fails. I back up daily to other NAS, so raid redundancy is a convenience for me, but not a necessity.

RAID-5 will of course work with SSDs, so there is no reason to think your approach won't work. Either way, it would be good if you post back on your results.