non-cached - Graham Perrin on Diigo

08 Feb 09

Compared to other physical formats, disk is ridiculously fragile and easily
corrupted/destroyed even when powered off
begging for disaster, because
it's not designed to work that way

18 Jan 09

Reliability 101 Part I: Reliability Concepts and Terminology

www.relex.com/...art_reliability101_1.asp - Preview

Diigo 9723 non-cached 2009

Mean Time To Failure (MTTF)
The average time to failure for a system that is not repairable
3 more annotations...
- Reliability
  The probability that the item will perform a required function without
  failure under stated conditions for a stated period of time. Reliability is significant because it
  takes into account time.
- reliability is expressed as a
  probability, it is always a value between 0 and 1.
- Unreliability is the complement of reliability. If your reliability
  is 0.9, the unreliability is equal to 0.1

MTTF versus MTBF

www.relex.com/...art_mttf.asp - Preview

Diigo 9723 non-cached 2009

for a non-repairable system, MTTF is equivalent to the mean of
its failure time
While MTBF is one of the most widely used metrics in reliability engineering, it is also one
that causes a great deal of confusion
3 more annotations...
- After restoration, the system may not be as good as new
- In most standards, MTBF is used to represent the mean time before
  failure
  - …before failure. - on 2009-01-18
  Add Sticky Note
- Even if a standard defines MTBF as the mean time between failures, it inherently
  means MTTF because MTTR is almost negligible
  - …between failures - on 2009-01-18
  Add Sticky Note

5th USENIX Conference on File and Storage Technologies - Paper

db.usenix.org/...index.html - Preview

Diigo 9723 non-cached 2009

7 Conclusion
As a first step
5 more annotations...
- analyzed disk replacement data from a number of
  large production systems, spanning more than 100,000 drives from
  at least four different vendors, including drives with SCSI, FC and
  SATA interfaces
- For drives less than five years old, field replacement rates were larger
  than what the datasheet MTTF suggested by a factor of 2-10
  - Shame on the manufacturers. - on 2009-01-18
  Add Sticky Note
- For five to eight year old drives, field replacement rates were a factor of 30 higher than what the datasheet
  MTTF suggested
  - Failure rates a factor of 30 (thirty) higher than the manufacturers' datasheets? Shame on them! - on 2009-01-18
  Add Sticky Note
- a continuous increase in replacement
  rates, starting as early as in the second year of operation.
- anecdotal evidence
  that bad batches are not unique to SATA disks

5th USENIX Conference on File and Storage Technologies – Abstract

www.usenix.org/...schroeder.html - Preview

Diigo 9723 non-cached 2009

field-gathered disk replacement data from a number of large production systems, including high-performance computing sites and internet services sites
annual disk replacement rates typically exceed 1%, with 2-4% common and up to 13% observed on some systems.
5 more annotations...
- field replacement is a fairly different process than one might predict based on datasheet MTTF
- early onset of wear-out degradation
- replacement rates in our data grew constantly with age
- assumed not to set in until after a nominal lifetime of 5 years
- one instance of a customer rejecting an entire population of disks as a bad batch, in this case because of media error rates

StorageMojo » Google’s Disk Failure Experience

storagemojo.com/...oogles-disk-failure-experience - Preview

Diigo 9723 non-cached 2009

drives look more reliable than what you and I see
results of accelerated life testing
11 more annotations...
- Vendors typically look at two types of data
- don’t do a good job of reflecting real world usage
- a drive tester consistently “green lights” a unit that invariably fails in the field
- a miracle if you see them in real life.
- your disk drive might crash without warning at any time
- SMART can warn you about some problems, but miss others, so you can’t rely on it. So don’t
- little correlation between disk workload and failure rates
- don’t worry about doing those daily backups to disk and other I/O intensive work
  - Side note: Time Machine backups to a nearby external drive can sometimes be near-endless and unbearably noisy.
    
    Factors include the mass of data at source and capacity of destination. (The larger and fuller a destination, the greater the time taken for Time Machine, Spotlight and other routines.) - on 2009-01-18
  Add Sticky Note
- failure rates do not increase when the average temperature increases
- SOHO users, consider replacing 3 year old disks, or at least get serious about back up.
- 24 Responses

StorageMojo » Everything You Know About Disks Is Wrong

storagemojo.com/...-you-know-about-disks-is-wrong - Preview

Diigo 9723 non-cached 2009

Maybe consumer stuff gets kicked around more
significant early onset of wear-out degradation
4 more annotations...
- drives just wear out steadily
- Instead replacement rates seem to steadily increase over time
- Drives get old, fast
- 99 Responses

Everything you know about disks is wrong - Computerworld Blogs

blogs.computerworld.com/5038 - Preview

Diigo 9723 non-cached 2009

Annual Failure Rates were quite a bit higher than vendor MTBF specs suggest
the best the Googlers observed was 1.7% in the first year, rising to over 8.6% in the third year
5 more annotations...
- If you get one of these errors, replace your drive, but not getting one doesn't mean you are safe. SMART is simply not reliable
- low utilization drives having slightly higher failure rates than high ulization ones.
- failure rates do not increase when the average temperature increases
- observed ARRs [Average Replacement Rate] range from 0.5% to as high as 13.5%. . . . up to a factor of 15 higher than datasheet AFRs. Most commonly, the observed ARR values are in the 3%range
- Drives are mechanical devices and wear out like machines

StorageMojo » NetApp Weighs In On Disks

storagemojo.com/...netapp-weighs-in-on-disks - Preview

Diigo 9723 non-cached 2009

Failure rates are several times higher than reported by drive companies
YMMV and often will if you deploy these disks in anything but the mildest of eval / demo lab environments
2 more annotations...
- consumer-class drives’ personality is determined by firmware that assumes the drive is isolated inside a laptop or desktop and cannot rely upon parity information stored on adjacent (peer) drives to recover from a partial or full error condition. Consequently, consumer drives exhibit “Type A” personalities as they heroically go offline for non-deterministic periods of time (a few seconds or many minutes), to “take charge” of the situation and perform various pre-programmed techniques attempting to resolve bad blocks, media / checksum errors, etc…
- many circumstances not restricted to age, environmentals (NVH), power & cooling, or even electro-mechanical behavior of drive peers within the same array, which can render a drive unusable – and eventually failed

StorageMojo » Open Letter to Seagate, Hitachi GST, EMC, HP, NetApp, IBM and Sun

storagemojo.com/...-gst-emc-hp-netapp-ibm-and-sun - Preview

Diigo 9723 non-cached 2009

Failure rates are several times higher than reported by drive companies
Drive failure rates rise steadily with age
1 more annotations...
- SMART is not a reliable predictor of drive failure

Page 2 - Hard Disk MTBF: Flap or Farce?

www.eweek.com/...1 - Preview

Diigo 9723 non-cached 2009

The current MTBF model isnt accounting accurately for how drives are handled in the field and how they function inside systems
IT budgets must include a line item for regular replacement of hard disks

Hard Disk MTBF: Flap or Farce?

www.eweek.com/...Hard-Disk-MTBF-Flap-or-Farce - Preview

Diigo 9723 non-cached 2009

annual disk replacements rates were more in the range of 2 to 4 percent
as high as 13 percent for some sites
1 more annotations...
- failure prediction models based on SMART parameters alone are likely to be severely limited in their prediction accuracy, given that a large fraction of our failed drives have shown no SMART error signals whatsoever

Hard Disk MTBF: Where's the Reliable Reliability Data? - News and Analysis by PC Magazine

www.pcmag.com/...0,2817,2105613,00.asp - Preview

Diigo 9723 non-cached 2009

disk replacement rates are much higher than predicted
SMART (self-monitoring, analysis and reporting technology) code in hard drives and storage management software—long touted by the industry as the best predictor of disk failure—was mostly a security blanket
- I have seen S.M.A.R.T. hard disk drive modules fail terribly with _no_ hint, from the hardware RAID into which the modules are plugged, that failure is occurring. - on 2009-01-18
- I'll vouch for this.
  
  A module that reports S.M.A.R.T. failure in one computer may offer no hint of failure in another computer. - on 2009-01-18
Add Sticky Note
1 more annotations...
- MTBF is just a statistical measure. We're not supposed to believe it.

Tips on preventing of data loss

www.cnwrecovery.co.uk/...prevention.html - Preview

Diigo 9723 non-cached 2009

Flash memory data recovery

www.cnwrecovery.co.uk/...flash_memory.html - Preview

Diigo 9723 non-cached 2009

Flash memory comes in several different physical packages
without an external battery and with no moving parts, are extremely robust
1 more annotations...
- Unless the chip is actually physically, or electrically damaged, CnW has a very high recovery success rate

FAQ CD & DVD

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Diigo 9723 non-cached 2009

Q) Why are disks unreadable

A) There are many answers
physical damage

FAQ Disks

www.cnwrecovery.co.uk/...faq_disks.html - Preview

Diigo 9723 non-cached 2009

Q This disk is not spinning, can you help?

A The answer is probably no.

14 Jan 09

ux: Mail reader

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Diigo 9723 non-cached 2009

synchronized scrolling. This is a separate idea

ux: Mail reader

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Diigo 9723 non-cached 2009

My apologies, I confused the two email threads for some reason, thinking
that this thread was the other one
my apologizes again for
2 more annotations...
- Sorry for the confusion
- Thanks for your patience

ux: Mail reader

ux.openoffice.org/...ReadMsg - Preview

Diigo 9723 non-cached 2009

Please disregard my email. I accidentally sent it while proofreading it,
and as it says at the bottom it was 2am when I wrote this. It may make no
sense. I will resend my response later.

Sorry
Please disregard my email. I accidentally sent it while proofreading it,
and as it says at the bottom it was 2am when I wrote this. It may make no
sense. I will resend my response later.

Sorry,
2 more annotations...
- Note to self: don't respond to
- emails at 2am ;-)

Graham Perrin's Library tagged non-cached → View Popular

Re: RAID is not a backup!

Reliability 101 Part I: Reliability Concepts and Terminology

MTTF versus MTBF

5th USENIX Conference on File and Storage Technologies - Paper

5th USENIX Conference on File and Storage Technologies – Abstract

StorageMojo » Google’s Disk Failure Experience

StorageMojo » Everything You Know About Disks Is Wrong

Everything you know about disks is wrong - Computerworld Blogs

StorageMojo » NetApp Weighs In On Disks

StorageMojo » Open Letter to Seagate, Hitachi GST, EMC, HP, NetApp, IBM and Sun

Page 2 - Hard Disk MTBF: Flap or Farce?

Hard Disk MTBF: Flap or Farce?

Hard Disk MTBF: Where's the Reliable Reliability Data? - News and Analysis by PC Magazine

Tips on preventing of data loss

Flash memory data recovery

FAQ CD & DVD

FAQ Disks

ux: Mail reader

ux: Mail reader

ux: Mail reader

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