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Pulled RAID 5 drives have very slow read speeds.

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Robert Goh
Pulled RAID 5 drives have very slow read speeds.
on Jan 30, 2014 at 7:27:23 pm

I just pulled 8 HUA721010KLA330 1TB drives from a RAID 5 because I'm upgrading to 2TB drives. I tested the file benchmark using HD Tune Pro. The read and write speeds range greatly from these identical drives. Write speeds range from 40MB/s to 80MB/s. Read speeds range from 10MB/s to 80 MB/s. I'm worried about the drives that have read speeds of 10MB/s and write speeds of 40+MB/s. Why such a difference in read and write speeds on the same drive? Why is the read speed so low? Crystaldiskinfo reports all drives are in good health. Hard drives are about 6 years old. Should I have done a normal format instead of a quick format before reusing them?


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Alex Gerulaitis
Re: Pulled RAID 5 drives have very slow read speeds.
on Jan 30, 2014 at 8:36:44 pm

According to the spec sheet, these should do between 40 and 80MB/s, so the 10MB/s read speeds you're reporting are odd.

How are these drives connected when you're running benchmarks, and on what system (CPU, OS, memory)?

-- Alex Gerulaitis | Systems Engineer | DV411 - Los Angeles, CA


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Robert Goh
Re: Pulled RAID 5 drives have very slow read speeds.
on Jan 30, 2014 at 8:57:13 pm

CPU i7-2600k, Windows 7 Ultimate, 16GB RAM. I'm connecting these drives via external USB 3.0 enclosures. I noticed the 10MB/s read only occurs when copying hundreds of GB of files. A few GB of transfer gave me 50MB/s read which is decent. There are no small files and it's 0% fragmented. Each video file is at least 100MB each, I have thousands of them. Maybe I should download a software to check the integrity of the slow hard drives for bad sectors. Any recommendations?


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Alex Gerulaitis
Re: Pulled RAID 5 drives have very slow read speeds.
on Jan 30, 2014 at 9:02:45 pm

There's a chance it's USB 3.0 messing up things. In itself it's fast, but the driver and overhead make the test less than clean. It's possible the drives will perform as they should via SATA.

Put the "slow" drive on a SATA port and test it. Only after that - think of other possible issues.


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Robert Goh
Re: Pulled RAID 5 drives have very slow read speeds.
on Jan 30, 2014 at 9:13:00 pm

OK I will connect via SATA and test. Some of the drives were able to read at 40-80MB/s from the same USB 3.0 enclosures however.


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Chris Murphy
Re: Pulled RAID 5 drives have very slow read speeds.
on Jan 31, 2014 at 3:44:19 am

Yes good point and actually it's likely SMART testing won't work through the USB bridge chipset anyway to see if there are reallocated or pending sectors.

This performance sounds like something is causing literally every file to be seeked at once, so the drive is just seeking to death. Read one or two big files at a time. Much bigger than 100MB. You need something about a gig in size for reads, and 2x RAM for writes to make sure OS caching isn't affecting the performance stat. But these days writes should be the same as reads.

A linux live CD will have tools that are useful for getting a decent (basic) idea of unbuffered drive read performance with hdparm or dd. dd is also available on OS X, use a bs size of at least 128k.


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Chris Murphy
Re: Pulled RAID 5 drives have very slow read speeds.
on Jan 31, 2014 at 3:37:31 am

smartmontools: GUI and command line versions for Windows. On Linux, lots of packages in your distro repo. And for Mac OS X, build via Macports and XCode. Also comes in handy for checking and setting SCT ERC. The command you want for a quick check is "smartctl -x /dev/sdX" which is a linux/bsd notation for the drive, I'm going to guess it's some letter on Windows.


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Chris Murphy
Re: Pulled RAID 5 drives have very slow read speeds.
on Jan 31, 2014 at 3:26:59 am

10MB/s isn't OK. Hitachi's data sheet on this model says that you should get 45-85MB/s. I'm not familiar with HD Tune Pro features, but you want to totally ignore random IO speeds. In fact, it's possible the sequential benchmark is useless depending on what the block size being tested is, and without knowing that and if it's similar to how the apps you use access storage, it's a pointless test. I'd think if you were really getting 10MB/s reads you'd have all sorts of problems with video editing, so I'm not sure I trust this test.

6 year old enterprise drives are at the end of their useful life. If they die in an array, what do you replace them with? Probably not the same thing, they're that old. So then you replace it with something similar, but probably totally different performance characteristics. Maybe it should be true you can mix and match drives, and with some raid implementations you can, I'd say it's only worth finding out if you're tinkering. Or if it's some kind of 2nd tier nearline backup: you spin the thing up, you write all the important stuff to it, and you spin it down, and you keep the system that runs it encased in carbonite, so that if you had to you could read it again in 3, 6, 12 or 18 months. But I wouldn't expect to get a lot more life out of the arrangement. If you have tape backup, I wouldn't even screw with it. Donate the drives. Heck I might take ~4, especially because I'd love to have more experience with exploding arrays due to face planting drives.


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Ron Amborn
Re: Pulled RAID 5 drives have very slow read speeds.
on Jan 31, 2014 at 10:21:16 pm

I agree with Chris about the 6 year old drives. We go through about 2-3 thousand drives per month and the one thing I can say is that depending on usage they all only last about 5 years or so if they are enterprise.And of course there are stories of drives lasting much longer at the users risk.
It is like your car tires, you replace them when they wear out and are potentially less dependable. Same goes for drives and all hardware, as it has a life span and if you push that limit you are open to more failure.I think the very low speeds you are seeing is a sign from above and you should switch before you have much worse problems.

Sincerely,
Ron Amborn President
Maxx Entertainment Digital
21562 Newland Street
Huntington Beach , Ca 92646
Direct 714-374-4944
Cell 714-713-4492 Fax 714-374-3404
ron@maxxdigital.com
http://www.maxxdigital.com




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