Hot Data Cache SSD life expectancy

Drobo - End of Sale Drobo 5N
1

I’ve just noticed that the SSD used for my “Hot Data Cache” now has a life expectancy of 97% — it was 100% a couple of days ago.
I’ve had my Drobo 5N (and its’ 128GB SSD cache) for about 41 days now. So on average the SSD is losing 1% of its life every 13 days or so.

That would mean a complete failure in about three and a half years. I’m not concerned about this, as the 5N would not lose any data when the SSD fails, it would just slow down, and fitting a new SSD is one of the easier DIY tasks.

I’m wondering if my experience is typical?

Hopefully someone will invent an SSD that doesn’t have this “degradation on write” issue in the next three years. What’s the betting on that?

2

That percentage is basically the range its guaranteed to work over…

its often around 1,000 full drive writes for consumer TLC, 3,000 for MLC and 6,000 or more for SLC

So if you have 100 GB TLC drive… you can write 100TB to it …

however… http://techreport.com/review/27909/the-ssd-endurance-experiment-theyre-all-dead some drives have gone on WAY WAY WAY past that

and look at the “ssd life estimation” here http://www.anandtech.com/show/8239/update-on-samsung-850-pro-endurance-vnand-die-size

its all very interesting academically…

i “know” this because i recently did some similar calculations / research… as i have a 256GB SSD in my server… and it gets about 120GB written to it each day… so its doing basically a full drive write every 48 hours… so suddenly that 1,000 writes works out to be 500 days / 1.6 years lifetime (did that in my head… its ballpark)

but actually i think its been set to 2,000 writes… as im only down to 95%…

its also interesting that if you look at the smart details for the drive… (i dont know if you can while its in drobo)… that the health counter’s RAW value (on my samsung drive anyway) … is the actual number of writes… so it might have a raw value of 66 (full drive writes) … which which would translate to say 95 (%) remaining…

either way i figures im not going to loose sleep over it… in the grand scheme they arent horribly expensive and in three years they will probably be relatively slow and obsolete anyway (and i’ll just ebay it… teehee)

3

[quote=“Docchris, post:2, topic:140742”]
its all very interesting academically… [/quote]
That’s mostly what’s driving me, especially as the 5N can run without the SSD in the “Hot Data Cache” socket, so I’ve nothing to fear when the SSD fails.

I’m wondering if the “Hot Data Cache” is for reads only, or if it caches writes as well? Does anyone know about this?

Caching writes requires some sort of UPS or battery backup, in case the power goes out after writing to the cache but before destaging it to the disks. I don’t think the 5N has its’ own battery, and I can’t see how it would know that it’s powered off my system UPS.

If writes are cached, then my nightly backups will be putting a significant write load on the cache, and that will accelerate the inevitable failure. It would be great to have an API that allowed me to disable the SSD cache overnight, to avoid this problem…

P.S. I’ve just noticed that I’ve scored “Reputation: 0”. I’ve always wanted to be disreputable.

4

I don’t think it does cache writes as there is nowhere to store that data redundantly (in case of SSD failure… not power failure), only the very large drobo’s (12 bay) that support 3 SSDs can cache writes

but reads from the drobo will cause the cache population to chance, resulting in significant writes to the SSD from the drobo

5

I’m using crucial 250GB card quite some time now in Drobo Mini, 5D and 5N, and its still indicating 100%.

As primary use, my Drobos are used for TimeMachine backups, so they really have to word pretty hard, as it has to make hourly backups for 3 Macs atm.

Secondary the Drobo’s are used to archive files. Those does not change that much.

In my opinion, the keyword is Trim, as it keeps SSD’s happy.

6

was it the trim feature that wasnt compatible in sandforce-based controllers?

7

I have my Drobo 5N now for 2 years with a Crucial m4 SSD 64GB mSATA module installed. It is almost daily in operation for my music, photo, and movie archives.
The lifetime of the mSATA module has now dropped to 1% and I’m expecting the message that I need to replace it every day…the new module is already waiting on my desk.

8

You don’t have to wait for it to fail before replacing it, you know. If it will allow you to sleep more soundly replace it today.

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[quote=“Swifty, post:3, topic:140742”]

According to the Drobo 5N web page, it does have a built-in battery.

[quote]Power Protecting Your Critical Data

The Drobo 5N doesn’t just protect from drive failures, it also includes a battery backup system that protects all data in memory or cache. That’s right, Enterprise grade data protection for you on your Drobo 5N! If power spontaneously goes away, the Drobo stays alive long enough for the data to be written to disk, ensuring your important information is always safe. The onboard battery recharges itself and is designed to last for the life of the product.[/quote]