and the difference in reliability between enterprise and consumer drives
. Today, Backblaze has spilled the beans on which drive
manufacturers are the most reliable.
The comparison is between Seagate, Hitachi, and Western Digital. (The
company has a few Toshiba and Samsung drives, but not enough for analysis.)
Backblaze says they buy the least expensive drives that perform well, based
on stress tests and a few weeks in production. As with the previous
analyses, Backblaze measured the reliability of the drives by looking at the
annual failure rate, the average number of failures while running a drive
for one year. Here is a pretty telling chart:
The company has also broken it down by drive model on their blog. The
Hitachi GST Deskstar (7K2000, 5K3000, and 7K3000) had the lowest annual
failure rates, from 0.9% to 1.1%. Meanwhile, the Seagate Barracuda Green had
a whopping 120% annual failure rate (an average age of 0.8 years). While
those were warranty replacement drives-likely refurbished ones already
used-the other Seagate drives had failure rates between 3.8% and 25.4%.
Overall, most of the drives survived for at least three years, but looking
at this data, you might want to consider going with a Hitachi or WD drive
instead of Seagate, unless you read other reviews of a specific drive’s
reliability.
Because Backblaze has a history of openness, many readers asked what drive
models work best and which last the longest. Given our experience with over
25,000 drives, they asked which ones are good enough that we would buy them
again. In this post, I’ll answer those questions.
Drive Population
At the end of 2013, we had 27,134 consumer-grade drives spinning in
Backblaze Storage Pods
. The breakdown by brand looks like this:
Hard Drives by Manufacturer Used by Backblaze
Brand
Number
of Drives
Terabytes
Average
Age in Years
Seagate
12,765
39,576
1.4
Hitachi
12,956
36,078
2.0
2,838
2,581
2.5
Toshiba
58
174
0.7
Samsung
18
18
3.7
As you can see, they are mostly Seagate and Hitachi drives, with a good
number of Western Digital thrown in. We don’t have enough Toshiba or Samsung
drives for good statistical results.
Why do we have the drives we have? Basically, we buy the least expensive
drives that will work. When a new drive comes on the market that looks like
it would work, and the price is good, we test a pod full
and see
how they perform. The new drives go through initial setup tests, a stress
test, and then a couple weeks in production. (A couple of weeks is enough to
fill the pod with data.) If things still look good, that drive goes on the
buy list. When the price is right, we buy it.
We are willing to spend a little bit more on drives that are reliable,
because it costs money to replace a drive. We are not willing to spend a lot
more, though.
Excluded Drives
Some drives just don’t work in the Backblaze environment. We have not
included them in this study. It wouldn’t be fair to call a drive “bad” if
it’s just not suited for the environment it’s put into.
We have some of these drives running in storage pods, but are in the process
of replacing them because they aren’t reliable enough. When one drive goes
bad, it takes a lot of work to get the RAID back on-line if the whole RAID
is made up of unreliable drives. It’s just not worth the trouble.
The drives that just don’t work in our environment are Western Digital Green
3TB drives and Seagate LP (low power) 2TB drives. Both of these drives start
accumulating errors as soon as they are put into production. We think this
is related to vibration. The drives do somewhat better in the new
low-vibration Backblaze Storage Pod
, but still not well enough.
These drives are designed to be energy-efficient, and spin down aggressively
when not in use. In the Backblaze environment, they spin down frequently,
and then spin right back up. We think that this causes a lot of wear on the
drive.
We measure drive reliability by looking at the annual failure rate, which is
the average number of failures you can expect running one drive for a year.
A failure is when we have to replace a drive in a pod.
blog-fail-drives-manufacture
This chart has some more details that don’t show up in the pretty chart,
including the number of drives of each model that we have, and how old the
drives are:
Number of Hard Drives by Model at Backblaze
Model
Size
Number
of Drives
Average
Age in
Years
Annual
Failure
Rate
Seagate Desktop HDD.15
(ST4000DM000)
4.0TB
5199
0.3
3.8%
Hitachi GST Deskstar 7K2000
(HDS722020ALA330)
2.0TB
4716
2.9
1.1%
Hitachi GST Deskstar 5K3000
(HDS5C3030ALA630)
3.0TB
4592
1.7
0.9%
Seagate Barracuda
(ST3000DM001)
3.0TB
4252
1.4
9.8%
Hitachi Deskstar 5K4000
(HDS5C4040ALE630)
4.0TB
2587
0.8
1.5%
Seagate Barracuda LP
(ST31500541AS)
1.5TB
1929
3.8
9.9%
Hitachi Deskstar 7K3000
(HDS723030ALA640)
3.0TB
1027
2.1
0.9%
Seagate Barracuda 7200
(ST31500341AS)
1.5TB
539
3.8
25.4%
Western Digital Green
(WD10EADS)
1.0TB
474
4.4
3.6%
Western Digital Red
(WD30EFRX)
3.0TB
346
0.5
3.2%
Seagate Barracuda XT
(ST33000651AS)
3.0TB
293
2.0
7.3%
Seagate Barracuda LP
(ST32000542AS)
2.0TB
288
2.0
7.2%
Seagate Barracuda XT
(ST4000DX000)
4.0TB
179
0.7
n/a
Western Digital Green
(WD10EACS)
1.0TB
84
5.0
n/a
Seagate Barracuda Green
(ST1500DL003)
1.5TB
51
0.8
120.0%
The following sections focus on different aspects of these results.
1.5TB Seagate Drives
The Backblaze team has been happy with Seagate Barracuda LP 1.5TB drives.
We’ve been running them for a long time – their average age is pushing 4
years. Their overall failure rate isn’t great, but it’s not terrible either.
The non-LP 7200 RPM drives have been consistently unreliable. Their failure
rate is high, especially as they’re getting older.
1.5 TB Seagate Drives Used by Backblaze
Model
Size
Number
of Drives
Average
Age in
Years
Annual
Failure
Rate
Seagate Barracuda LP
(ST31500541AS)
1.5TB
1929
3.8
9.9%
Seagate Barracuda 7200
(ST31500341AS)
1.5TB
539
3.8
25.4%
Seagate Barracuda Green
(ST1500DL003)
1.5TB
51
0.8
120.0%
The Seagate Barracuda Green 1.5TB drive, though, has not been doing well. We
got them from Seagate as warranty replacements for the older drives, and
these new drives are dropping like flies. Their average age shows 0.8 years,
but since these are warranty replacements, we believe that they are
refurbished drives that were returned by other customers and erased, so they
already had some usage when we got them.
Bigger Seagate Drives
The bigger Seagate drives have continued the tradition of the 1.5Tb drives:
they’re solid workhorses, but there is a constant attrition as they wear
out.
2.0 to 4.0 TB Seagate Drives Used by Backblaze
Model
Size
Number
of Drives
Average
Age in
Years
Annual
Failure
Rate
Seagate Desktop HDD.15
(ST4000DM000)
4.0TB
5199
0.3
3.8%
Seagate Barracuda
(ST3000DM001)
3.0TB
4252
1.4
9.8%
Seagate Barracuda XT
(ST33000651AS)
3.0TB
293
2.0
7.3%
Seagate Barracuda LP
(ST32000542AS)
2.0TB
288
2.0
7.2%
Seagate Barracuda XT
(ST4000DX000)
4.0TB
179
0.7
n/a
The good pricing on Seagate drives along with the consistent, but not great,
performance is why we have a lot of them.
Hitachi Drives
If the price were right, we would be buying nothing but Hitachi drives. They
have been rock solid, and have had a remarkably low failure rate.
Hitachi Drives Used by Backblaze
Model
Size
Number
of Drives
Average
Age in
Years
Annual
Failure
Rate
Hitachi GST Deskstar 7K2000
(HDS722020ALA330)
2.0TB
4716
2.9
1.1%
Hitachi GST Deskstar 5K3000
(HDS5C3030ALA630)
3.0TB
4592
1.7
0.9%
Hitachi Deskstar 5K4000
(HDS5C4040ALE630)
4.0TB
2587
0.8
1.5%
Hitachi Deskstar 7K3000
(HDS723030ALA640)
3.0TB
1027
2.1
0.9%
Western Digital Drives
Back at the beginning of Backblaze, we bought Western Digital 1.0TB drives,
and that was a really good choice. Even after over 4 years of use, the ones
we still have are going strong.
We wish we had more of the Western Digital Red 3TB drives (WD30EFRX).
They’ve also been really good, but they came after we already had a bunch of
the Seagate 3TB drives, and when they came out their price was higher.
Western Digital Drives Used by Backblaze
Model
Size
Number
of Drives
Average
Age in
Years
Annual
Failure
Rate
Western Digital Green
(WD10EADS)
1.0TB
474
4.4
3.6%
Western Digital Red
(WD30EFRX)
3.0TB
346
0.5
3.2%
Western Digital Green
(WD10EACS)
1.0TB
84
5.0
n/a
What About Drives That Don’t Fail Completely?
Another issue when running a big data center is how much personal attention
each drive needs. When a drive has a problem, but doesn’t fail completely,
it still creates work. Sometimes automated recovery can fix this, but
sometimes a RAID array needs that personal touch to get it running again.
Each storage pod runs a number of RAID arrays. Each array stores data
reliably by spreading data across many drives. If one drive fails, the data
can still be obtained from the others. Sometimes, a drive may “pop out” of a
RAID array but still seem good, so after checking that its data is intact
and it’s working, it gets put back in the RAID to continue operation. Other
times a drive may stop responding completely and look like it’s gone, but it
can be reset and continue running.
Measuring the time spent in a “trouble” state like this is a measure of how
much work a drive creates. Once again, Hitachi wins. Hitachi drives get
“four nines” of untroubled operation time, while the other brands just get
“two nines”.
Untroubled Operation of Drives by Manufacturer used at Backblaze
Brand
Active
Trouble
Number of Drives
Seagate
99.72
0.28%
12459
Western Digital
99.83
0.17%
933
Hitachi
99.99
0.01%
12956
Drive Lifetime by Brand
The chart below shows the cumulative survival rate for each brand. Month by
month, how many of the drives are still alive?
blog-36-month-drive-survival-rate
Hitachi does really well. There is an initial die-off of Western Digital
drives, and then they are nice and stable. The Seagate drives start strong,
but die off at a consistently higher rate, with a burst of deaths near the
20-month mark.
Having said that, you’ll notice that even after 3 years, by far most of the
drives are still operating.
What Drives Is Backblaze Buying Now?
We are focusing on 4TB drives for new pods. For these, our current favorite
is the Seagate Desktop HDD.15 (ST4000DM000). We’ll have to keep an eye on
them, though. Historically, Seagate drives have performed well at first, and
then had higher failure rates later.
Our other favorite is the Western Digital 3TB Red (WD30EFRX).
We still have to buy smaller drives as replacements for older pods where
drives fail. The drives we absolutely won’t buy are Western Digital 3TB
Green drives and Seagate 2TB LP drives.
A year and a half ago, Western Digital acquired the Hitachi disk drive
business. Will Hitachi drives continue their excellent performance? Will
Western Digital bring some of the Hitachi reliability into their
consumer-grade drives?
At Backblaze, we will continue to monitor and share the performance of a
wide variety of disk drive models.]]>
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