Will adding a 15k SAS on a storage make speed difference ?

lianne143
lianne143 used Ask the Experts™
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Hi,

We are having a new Dell ME4024SAN specced out and they have quoted for 10k SAS disks( 10x1.8 HDD 10k 512e SAS 12 2.5) and also they have added 2.62TB ssd for auto tiering.
If I go with 15k SAS dHardisk  and will it make noticeable speed difference.
Any  help much appreciated
Thanks
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Senior Developer
Commented:
In some use-cases? For sure. But do they apply to your requirements? I don't know. It depends on what kind of data needs to be read and written.

E.g. when it's real auto-tiering on the SSD's, then the data move back to SAS Is faster. Thus changes are faster active. If the SSD is just a read-cache, then writes will be still faster. And of course reads on non-SSD backed data is also faster.

But whether these performance gains are worth the money strongly depends on your use-case of that storage. This includes the kind of data, the access patterns and the number of users working on this device. I would guess, when 80% of the requests can be satisfied by the SSD's then it is not worth the money. But when there is much more traffic on the disks itself, then you may need to calculate some time-loss for each user per day over the amortization period due to latency. This can add up to some amounts in the 1k - 10k range or sometimes more. So spending the money disks from the beginning may give you some calculated ROI and happier users.
SteveArchitect/Designer

Commented:
Yes 15K disks are 'faster' that 10K disks but it depends what you;re going to do with them as it may not offer sufficient benefit to justify the cost.
On a RAID set with 10 disks you;'re going to get pretty good read/seek times from 10K disks anyway so you may only see a big difference with 15K disks if you are really hammering them and your RAID controller can make the most of the higher throughput.
Philip ElderTechnical Architect - HA/Compute/Storage

Commented:
Current generation 10K SAS disks have an areal density so high that the extra spindle speed is essentially negated.

Are 15K 2.5" SAS drive even made anymore? Some manufacturers are dropping both 15K and 10K rust altogether.
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Top Expert 2014

Commented:
Yes Philip, they still make 15K SFF disks.
Philip ElderTechnical Architect - HA/Compute/Storage

Commented:
@andyalder Wow. The only place we're deploying rust today is in 60-bay and 102-bay JBODs for high density. Flash is still too expensive per Gigabyte though prices have been dropping quite a bit recently. I want to see those 32TB and 60TB+ flash drives manufacturers are promising!
kevinhsiehNetwork Engineer

Commented:
15K drives have hit the end of the line, and there is no more R&D into them. Manufacturing is stopping. 10K drives have significantly greater capacity, so instead of looking at 15K drives, I would look to add more flash instead. Flash is killing 15K drives because flash is faster and cheaper than 15K when using recommended RAID levels appropriate for the disks (RAID 10 for 15K disks, RAID 5 for flash).

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