Can I RAID with mixed SanDisk SSDs?

[Boddy]

I'm looking to set up a 8 disk (maybe 16 disks) RAID 6 for a wiki project I had in mind.

I have purchased several SanDisk Ascend SAS SSDs but I have noticed that the seller has included some SanDisk Eco SAS SSDs. Both seem to use 19 nm eMLC

The disks are same size and similar performance (not exactly the same), but the Eco disks are rated at 3 DWPD and Ascend at 10 DWPD.

Could I set up a RAID 6 with using both Ascend and Eco disks or am I really better of using identical disks?

Could using different disks in my case potentially give me additional problems.

Many thanks in advance for your help.

 

[William]

You can but performance of the whole Raid will drop to the lower performing drive.

 

[MiniKnight]

TBH, if you just want to make it easy, you'll probably be OK. The disks are close enough performance wise that it won't matter much and I doubt you'll have that much writes to the Wiki where you'll be at 3DWPD even writing parity blocks.

The Ascends are higher endurance drives so you might just want them for that purpose. From a pure will it work standpoint you should be fine.

 

[Boddy]

You can but performance of the whole Raid will drop to the lower performing drive.

Thanks so much William for your feedback and clarification.
Much appreciated.

 

[Boddy]

TBH, if you just want to make it easy, you'll probably be OK. The disks are close enough performance wise that it won't matter much and I doubt you'll have that much writes to the Wiki where you'll be at 3DWPD even writing parity blocks.

The Ascends are higher endurance drives so you might just want them for that purpose. From a pure will it work standpoint you should be fine.

Many thanks MiniKnight for your detailed and insightful feedback, it is very much appreciated.

Regarding endurance:
Would you expect the Ascend drives with 10 DWPD to have a longer life than the Eco drives with 3 DWPD?
Or would you expect the may have similar life but the Ascend 10 DWPD are geared to work harder?

 

[Patrick]

What do you mean by life?

 

[Boddy]

What do you mean by life?

I meant longer 'lifespan'.
Although they share same MTBF, can bigger DWPD translate to longer lifespan?

 

[Patrick]

I meant longer 'lifespan'.
Although they share same MTBF, can bigger DWPD translate to longer lifespan?

Well, the simple answer is yes if you are writing enough to the drives But generally I would imagine from a pure, if they were both used at 1DWPD for 5 years you would see the same type of failure rate between the two.

 

[EffrafaxOfWug]

Technically better to use matched discs but should be of little consequence with fairly little in the way of differences in random IO between the different drives. Is this going to be a wiki database or a wiki datastore? Assuming softraid, personally I'd eliminate the parity overhead and go for RAID10 (especially if this is for a DB so as to avoid continual RMW thrashing) but then I'm a RAID10 fanboy.

Although they share same MTBF, can bigger DWPD translate to longer lifespan?

When it comes to storage, MTBF stands for "Meaningless Term; Backups Foremost". Using MTBF to measure reliability and lifespan is like making a stew; everything goes to pot.

Base your decision on the expected workload, expected lifespan and DWPD... and if you're unlikely ever reach 3 or even 1 DWPD just stick with the cheapest price per gig.

 

[Boddy]

Well, the simple answer is yes if you are writing enough to the drives But generally I would imagine from a pure, if they were both used at 1DWPD for 5 years you would see the same type of failure rate between the two.

Many thanks Patrick for clarifying this point.

Considering that I have a few projects in mind and I'm not 100% certain of the use at this stage,
Even though I picked up the drives for $0.34 G/b, I think I'll see if seller with exchange for the drive I originally ordered and not supply a cheaper substitute.

 

[Boddy]

Technically better to use matched discs but should be of little consequence with fairly little in the way of differences in random IO between the different drives. Is this going to be a wiki database or a wiki datastore? Assuming softraid, personally I'd eliminate the parity overhead and go for RAID10 (especially if this is for a DB so as to avoid continual RMW thrashing) but then I'm a RAID10 fanboy.



When it comes to storage, MTBF stands for "Meaningless Term; Backups Foremost". Using MTBF to measure reliability and lifespan is like making a stew; everything goes to pot.

Base your decision on the expected workload, expected lifespan and DWPD... and if you're unlikely ever reach 3 or even 1 DWPD just stick with the cheapest price per gig.

Thanks EffrafaxOfWug for your insightful and accurate feedback .
What I have in mind is a dynamic collaborative wiki/forum.
I'm planning to use the 'meetup' platform to collaborate a design team between some IT, Knowledge Management, Gamification and Design gurus. I'm expecting awesomeness and to make a real difference to policy making process in my country and abroad.

 

[Boddy]

PS. Thanks to everyone who has given feedback and information, your feedback is greatly appreciated and highly regarded.
Whilst I'm not an IT expert, you have provided some valuable knowledge and enabled greater feasibility in achieving success in this project.
Thank you all so much!