Solidigm has released a 10-year Total Cost of Ownership (TCO) model showing a VAST Data/Solidigm SSD system supporting 1 EB of data costs 58.9 percent less than an equivalent disk drive-based Ceph/Seagate system.
It is detailed in a white paper, The Economics of Exabyte Storage written by Dave Sierra, who holds a Product Messaging and Positioning, Sustainability, position at Solidigm.
Sierra says: “This white paper demonstrates through rigorous, verifiable analysis that … The Solidigm + VAST solution delivers an estimated 10-year hardware and OpEx TCO of approximately $35.19 million USD, representing a substantial 58.9 percent saving compared to the HDD/CEPH solution’s calculated TCO of $85.62 million USD.”
The calculation is split into hardware, power and space components;
He only looks at hardware and allied operating expenses and not the software and networking side of things. Because it’s a VAST Data system, the Ceres SSD enclosures, fitted with 122 TB QLC Solidigm SSDs, have a 10-year operating life, as that’s what VAST Data warrants. The Ceph system storage enclosures are filled with Seagate Exos Mozaic 3+ 30TB disk drives, and these are replaced twice during the model’s 10-year span. That’s because “empirical data from large-scale deployments, such as those reported by Backblaze, consistently shows that HDD Annualized Failure Rates (AFR) tend to increase significantly after the third to fifth year of operation, entering the “wear-out” phase of the bathtub curve. … Therefore, aligning with common enterprise practices for mission-critical systems and mitigating the impact of rising failure rates, this TCO model assumes a 4-year refresh cycle for the HDDs.”
That means the model assumes that the HDDs are refreshed two times, costing more, while the SSDs are not refreshed at all. Sierra says: “The significant difference in assumed operational lifespan—requiring two full replacements for the HDD fleet versus none for the SSDs over 10 years—is a fundamental factor driving the TCO divergence.”
The 1 EB of data requires a filesystem metadata and data protection overhead. This means that there is actually 1.25 EB of HDD capacity whereas, because of VAST’s 2.5:1 deduplication/compression ratio and generally lower erasure coding overheads, there is 0.456 EB of actual SSD capacity, meaning 2.74x more disk capacity. The net result is 41,667 disk drives, in 1,852 RU (52 racks), are needed vs 3,738 Solidigm SSDs in 170 RU (5 racks). Some people might think this is stacking the deck.
Sierra says: “This fundamental difference in required physical hardware drives downstream reduction on component counts, capital costs, power consumption, and space utilization.”
The disk drive HW refreshes add a lot of extra cost, as a table shows;
We can respectfully take issue with this as Backblaze has recently extended the operational life of its disk drives. CFO Marc Suidan told analysts: “We evaluated the estimated useful life of our fixed assets based on more recent operational data and found that our hardware last an estimated six years instead of the three to five years estimate that what we previously were using.”
Let’s modify Sierra’s table and add a single HDD refresh at the 6-year point costing the average of his year 4 and year 8 costs; $10.91 million. That changes the total 10-year HDD hardware cost to $29.86 million, only $800,000 more than the SSDs.
That would, in turn, change the total 10-year TCO figure for the HDDs from $85.62 million to $74.71 million, a 52.9 percent difference from the Solidigm SSD TCO total, not 58.9 percent. It’s still substantial.
At this point, we can ask a question. If Sierra’s estimates are correct, then why is Backblaze not replacing its 321,201 disks under management with 122 TB Solidigm QLC SSDs, using VAST-like SW to give them the same effective capacity with far fewer drives?
The VAST software costs a lot of money and you can’t simply use the data reduction and metadata management part of it alone, junking the rest. Absent that you would have to have 1.25EB of raw SSD capacity, not Sierra’s 0.456 EB, putting the SSD acquisition cost up to the $60 million mark and raising the 10-year SSD TCO from $35.19 million to $66.13 million. This would be 11.5 percent less than the $74.71 million HHD cost with a single refresh cycle.
Sierra’s SSD vs HDD cost calculation for Solidigm is dependent on the use of VAST Data software and, it appears, an overly low view of HDD working life. Take these two things away and the Solidigm/VAST 10-year TCO model is not generally applicable outside the VAST customer base.
Bootnote
Qumulo President and CEO Doug Gourlay sent us his thoughts about this study.
He said: “I know some of the newer entrants into the storage/data landscape don’t have enough fleetwide data to use so they may have to look for external rubrics to identify refresh and replacement cycles of components such as HDDs – thus the convenient ‘you have to refresh HDDs every four years’ and ‘you can use QLC for 10 years’.
“So I did some digging across our fleetwide statistics that now span 13 years and 1000s of systems – a far larger and longer-lived dataset than available to smaller companies, but found the following HDD failure rates in 2023/2024:
- 2023 HDD failure rate, fleet-wide was 0.56% and the SSD failure rate was 0.47% ,
- 2024 HDD failure rate fleet-wide was 0.65% and the SSD failure rate was 0.37%
“These are statistically similar, although certainly favoring SSD and encompasses SSD and HDD that are 10+ years in deployed life.
“Similarly though, Solidigm, the manufacturer of the HDDs, who makes them in the Dalian fab in the People’s Republic of China, only warrants their QLC for 5 years, yet is trying to claim 10 years of useful life in the article you published.
“There are a few other issues, but the above are the main ones that caught my eye and may be worth a clarification from the editor.”
Glad to oblige.
