15K RPM SAS Hard Drives

What 15,000 RPM buys and costs

A faster spindle cuts the wait for data to rotate under the head. Seagate's 15K data sheet rates the class at 2.0 ms average latency and 300 to 210 MB/s sustained transfer, against 2.9 ms for its 10K drives, and names OLTP, databases and other transaction-based applications as the best fit. The cost is capacity: Seagate's 15K family stops at 900GB in 2.5-inch.

Power draw is close between the classes: Seagate's data sheets give its 15K drives 6.9 to 7.6 W of operating power and its advanced-format 10K drives 6.9 to 8.6 W, so what the extra speed costs is capacity per bay.

A 12Gb/s controller runs each older SAS generation at its own rate:

Older drives keep working on newer controllers: Broadcom's 12Gb/s SAS HBAs support 3, 6 and 12Gb/s link rates, and a 12Gb/s 15K drive negotiates 3.0, 6.0 or 12.0 Gb/s on each port. What decides the fit is the carrier and the backplane, not the generation.

15K SAS or SSD

When latency is the limit, a SAS SSD in the same bay beats any 15K drive, because it has no platter to wait on; when the job is replacing a drive in an existing 15K array, a 15K drive keeps the set uniform. KIOXIA's 24G SAS SSDs come in a one-drive-write-per-day line from 1.92TB to 30.72TB and a three-per-day line from 1.6TB to 12.8TB, so check the write volume against those classes before you swap a 15K array for flash. Both kinds run on the same SAS controllers.

15K drives fit the 2.5-inch bays on 2.5-inch hard drives and run behind server RAID controllers; for laying out the array itself, read our article on choosing a RAID level.

Servers and alternatives

Dell's R750 supported-drive list includes a 900GB 12Gb SAS 15K 2.5-inch drive, and HPE's DL380 Gen10 QuickSpecs list 15K Enterprise SAS drives at 300GB, 600GB and 900GB, so the 15K class appears on the supported lists of both servers. For more capacity per bay, step to 10K RPM SAS drives; for bulk storage, NL-SAS; and SAS SSDs use the same SAS bays and controllers. Every 15K drive also appears in SAS hard drives, and each comes with an Enterasource warranty for the period shown on its listing.

15K drive questions

Is a 15K drive faster than a 10K drive?

Yes, for random access. Seagate rates its 15K drives at 2.0 ms average latency and 300 to 210 MB/s sustained transfer on 512-native models, against 2.9 ms and up to 266 MB/s for its 10K drives. The 10K drive holds more: 2.4TB against 900GB at the top of each 2.5-inch line. Pick 15K when response time matters more than space.

Should I use 15K SAS drives or SSDs?

Use SSDs when you need the lowest latency or more capacity per bay, since a SAS SSD has no rotational delay and reaches far beyond 900GB. Use 15K drives to repair or extend an array already built on them, or where a system's support list names 15K drives. Both connect to the same SAS RAID controllers and HBAs, so the choice does not change the controller.