SAS SSD vs SATA SSD: Link Speed, Dual Port, Power and What Each Costs in the UK

SAS SSD vs SATA SSD: Samsung PM1643 against PM893

Comparing interfaces is easiest with one maker's drives side by side, so this page sets Samsung's PM1643, a 12G SAS SSD, against its PM893 SATA SSD. The PM1643 runs from 960GB to 30.72TB and the PM893 from 240GB to 7.68TB, so the two overlap from 960GB to 7.68TB. The figures are Samsung's own, from two documents with their own test conditions, so read them as maker ratings rather than a like-for-like test.

The PM1643 brochure also states an uncorrectable bit error rate of 1 sector per 10^17 bits read. We have not found a Samsung statement of that rate for the PM893, so the two cannot be set side by side on that measure.

SAS vs SATA SSD speed: checking Samsung's 4x claim against its own sheets

Samsung says the PM1643 delivers read and write performance more than four times what SATA is capable of. Its own two sheets let us check that, with the caveat about test conditions above.

• Sequential read: 2,100 against 550 MB/s, about 3.8 times.
• Sequential write: 2,000 against 520 MB/s, about 3.8 times.
• Random read: 450,000 against 98,000 IOPS, about 4.6 times.
• Random write: 70,000 against 30,000 IOPS, about 2.3 times.

Those ratios are our arithmetic. On these figures the claim is close on sequential transfers, holds on random reads and falls well short on random writes. A server that mostly reads gains the most from the SAS drive; one that does many small writes gains about twice the rate rather than four times.

The 12 Gbps link is not the newest SAS either. KIOXIA lists its current SAS SSDs as SAS-4 at 22.5 Gbit/s, so a 12G drive such as the PM1643 sits a generation behind the fastest SAS link, while the PM893's SATA link is 6 Gb/s.

Dual port and failover: what a SAS SSD adds

Samsung says the PM1643 supports dual-port functionality, giving two access paths to the storage array controller. SNIA, writing about 24G SAS, describes native failover and dual-port features that allow multiple domains to be configured. We have not found a Samsung statement of dual-port support for the PM893.

The second path only helps if your system is built to use it, so check your array or server documents before paying for it. If the drive will sit behind a single controller path, the dual port is not the reason to choose SAS.

Power, drive height and power-loss protection in Samsung's pair

In this pair the faster drive costs power. At 13.5 W active, the PM1643 draws about four times the PM893's 3.2 W active write figure, and its 5 W idle is more than three times the PM893's 1.5 W. That is our arithmetic on Samsung's sheets, about these two drives rather than SAS and SATA as a whole, and it adds up across a full shelf.

Height is the other physical difference between them. The PM1643 is 15 mm thick and the PM893 7 mm, so a bay that only takes 7 mm drives cannot hold the PM1643. Check the drive height your caddy or bay accepts in the server's own documents.

On power loss, Samsung says the PM1643 is designed to prevent data loss from unexpected shutdowns with its power-loss protection architecture. We have not found a Samsung statement on power-loss protection for the PM893, so do not assume it either way; ask for the maker's document if you need it.

Mixing drives, and SAS HDD vs SATA SSD

Seagate's knowledge base says SATA drives may be plugged into SAS controllers. So a SATA SSD can go into a SAS system, and choosing SATA does not rule out a SAS server. We have not found a document stating the reverse, a SAS drive on a SATA-only controller.

Some readers weigh a SAS hard drive against a SATA SSD. Both can sit on a SAS controller, on Seagate's statement, but we have not found a pair of maker sheets that would compare a SAS hard drive with a SATA SSD fairly, so this page prints no figures for that choice. The SAS vs SATA page compares the two interfaces for hard drives, and the SAS hard drives page lists them.

SAS SSD and SATA SSD prices on Amazon.co.uk

The two tables below set the SAS side against the SATA side, in pounds sterling inc VAT and sorted per TB. The SAS table holds 2 listings right now. The SATA table holds 12 listings. Each row shows its condition, new or used.

When the SAS table holds only a few rows, the choice in practice can come down to what is in stock. Before you press Buy on Amazon, check the interface and drive height in the listing against your bay. The SAS SSD page goes through SAS part numbers, and the Samsung PM893 page covers the SATA drive used here.