Re: ZFS performance (was: Re: deduplicating file systems: VDO withDebian?)
Jeffrey Walton wrote:
> On Fri, Nov 11, 2022 at 2:01 AM <tomas@tuxteam.de> wrote:
> >
> > On Fri, Nov 11, 2022 at 07:15:07AM +0100, hw wrote:
> > > On Thu, 2022-11-10 at 23:05 -0500, Michael Stone wrote:
> >... Here's a report
> > by folks who do lots of HDDs and SDDs:
> >
> > https://www.backblaze.com/blog/backblaze-hard-drive-stats-q1-2021/
> >
> > The gist, for disks playing similar roles (they don't use yet SSDs for bulk
> > storage, because of the costs): 2/1518 failures for SSDs, 44/1669 for HDDs.
>
> Forgive my ignorance... Isn't Mean Time Before Failure (MTFB) the
> interesting statistic?
>
> When selecting hardware, like HDD vs SSD, you don't know if and when a
> failure is going to occur. You can only estimate failures using MTBF.
>
> After the installation and with failure data in hand, you can check if
> the MTBF estimate is accurate. I expect most of the HDD and SSD
> failures to fall within 1 standard deviation of the reported MTBF. And
> you will have some data points that show failure before MTBF, and some
> data points that show failure after MTBF.
You'd like that to be true. I'd like that to be true. What do we
actually see?
Here's Western Digital's new 22TB 7200RPm NAS disk:
https://documents.westerndigital.com/content/dam/doc-library/en_us/assets/public/western-digital/product/internal-drives/wd-red-pro-hdd/product-brief-western-digital-wd-red-pro-hdd.pdf
Claimed MTBF: 1 million hours. Believe it or not, this is par
for the course for high-end disks.
24 hours a day, 365 days a year: 8760 hours per year.
1000000/8760 = 114 years.
So, no: MTBF numbers must be presumed to be malicious lies.
More reasonable: this drive comes with a 5 year warranty. Treat
that as the expected lifetime, and you'll be somewhat closer to
the truth.... maybe.
Here's a new number that used to be just for SSDs, but is now
for spinners as well: expected workload (per year) or Total TB
Written (lifetime). For the above disk family, all of them claim
300TB/year. That's a little bizarre: it's 9.51 MB/s. Modern
high end spinners also claim 200MB/s or more when feeding them
continuous writes. Apparently WD thinks that can't be sustained
more than 5% of the time.
-dsr-
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