Performance throttling SF1200 drives
Performance throttling ensures that sufficient PE cycles are available for the duration of the warranty and is based on a PE life curve over time.
Time is based on "power on hours", therefore power on hours without write activity enables credits to be incurred.
There are four choices that a SF vendor can choose from for the warranty duration:
No throttling
1 year warranty
3 year warranty
5-year warranty
If no throttling is selected the controller will not ensure that the PE cycles last for a predefined duration. (From testing carried out to date in the endurance thread only OCZ have elected to impliment LTT. Drive tested from Corsair and Mushkin in th eendurance thread have not had LLT).
When a drive is brand new the controller is configured to allow "credits". Credits allow PE wear without inducing throttling. The credit duration can also be configured. As standard it is 2% of the drives warranty period. During this period the drive will not be performance throttled regardless of the warranty duration.
Once those credits have expired throttling is implemented if PE cycles exceed the warranty duration.
Throttling will never allow PE cycles to fall below the life curve. This can result is a significant slowdown in write speeds. Once this has occurred the only way to recover the drive is to leave it to idle until such time that the PE cycles are aligned back with the life curve.
Throttling is not deactivated at the end of the defined warranty period.
There is no information on workloads that can induce throttling, however it is important to note that for typical Client workloads it is unlikely that the drive will be subject to throttling.
Wear is based on PE cycles and is not related to host writes. If highly compressible data is written it has little impact on PE cycles. This enables a fully throttled drive to still achieve peak performance if highly compressible data is written.
The recovery period (idle time) can be quite short before throttling is released. If significant write activity occurs again however the drive will quickly revert back to a throttled state.
For non compressible data the impact of throttling resulted in write speeds being capped at ~6MB/s. For 0fill write speeds are not impacted.
In addition to life time throttling there is also a throttling mechanism that throttles burst activity. So far this has not been investigated in this thread.
The best estimate for the amount of writes that can be incurred without LTT becoming an issue: (Assuming the SSD is powered up 24/7)
• 0.60TiB per day with 1 year throttle/ 25.6GiB per power on hour/ 7.28MiB/s
• 0.2TiB per day with 3 year throttle/ 8.53GiB per power on hour/ 2.42MiB/s
• 0.12TiB per day with 5 year throttle/ 5.12GiB per power on hour/ 1.45MiB/s
Power throttling
Similar in operation to performance throttling, but here power consumption is monitored, based on flash program, erase, or read operation activities Variable settings can be configured by the vendor from no power throttling to frugal power throttling.
SMART attributes #233 (E9) and #242 (F1)
Attribute #233 records the write to NAND.
Attribute #242 records host writes.
Dividing #233 by #242 will show the compressibility and write applification factors that the controller has achieved against writes incurred by the host.
For SF1 drives these attributes are only updated every 64GB.
For SF2 drives these attributes are updated ever GB
The lower the ratio the higher the compression factor = less writes to NAND and faster write speeds.
Uncompressible 4K random writes induce significantly more writes to NAND than writes incurred by the host system. (Amplification factor of 3.3)
TRIM
It would appear that without TRIM more writes to NAND are incurred.
It would appear that write performance is enhanced without TRIM until the drive becomes degraded. Once the drive is degraded write speeds drop to around 50% below what could be expected if TRIM was activated. This "impact" is however highly subjective to workload so YMMV.
Performance throttling SF2xxx drives
General note. SMART reading are taken at a point in time and not necessarily when an attribute value changed. Consequently variations between readings can be expected. Readings can however be averaged out.
E6 raw value
The Vertex 3 has a new SMART attribute - E6. The raw 1byte value appears to indicate a reduction in the life curve count ranging from 120 to 0. During the endurance test the reduction in life curve attribute was linear against the writes being incurred.
The average amount of writes to generate a drop in the E6 value = 261GB.
This is based on the workload from the endurance app. A more onerous workload would reduce this figure and a less onerous work load would increase it.
The total amount of data that can be written between 120 & 0 values = 34TB
E7 Life left (MWI)
It would appear that E7 - Life Left is directly linked to E6. If the amount of PE cycles recorded by E6 exceeds the E7 value to maintain PE for the warranty duration the drive will become throttled until such time as E7 can recalibrate.
The MWI dropped to 99% at 11,078GB. Averaging out subsequent drops in the MWI vs writes to establish a theoretical figure for 100%, resulted in a figure of 8,592GB. it would appear that 8,592GB was therfore the amount of data that could be written within the credit period.
If this figure is excluded the MWI projection for write capacity = 283TB
The ratio difference in projections between E6 & E7 = 8.32.
It would appear that the write load is 8.32 times higher than the the life time curve can accomodate to maintain the warranty duration.
Compression
The V3 update frequency for SMART attributes E9 & F1 is 1GB. This allows compression factors to be better calculated.
Write speeds (and to an lesser extent read speeds) are dependent on how compressible the data is. Write speeds were detemined using Anvil's Benchmark App. Interestingly the V3 was slower at sequential writes that an X25-M if the data was not highly compressible, but for 4K it was faster regardless of the compression factor.
Depending on the compressibility factor of the data a SF drive can been faster or slower that drives that don't use compression.
Testing by Vapor
RAISE
RAISE - Redundant Array of Independent Silicon Elements - writes data across multiple flash die to enable recovery from a failure in a sector, page or entire block, just like the concept of multi-drive RAID used in disk-based storage, but RAISE only requires a single drive.
SSDs are built using flash die that are assembled up to 8 die per package. For optimum capacity the SSD can be assembled with up to 16 packages. That puts 128 individual die in one SSD. If the failure rate (unrecoverable read error) of one MLC die is conservatively 1,000 PPM (a failure probability of 0.1%) then using the probability formula for 128 devices the failure rate increases to 12.0% over the life of the SSD.
Using RAISE technology in a SandForce Driven SSD reduces the probability of a single unrecoverable read error by 100 times to 0.001%. Applying that same formula, the failure rate of the SSD drops from 12.0% to a mere 0.13%, nearly 100 times lower.
SF2xxx drives now have an option to disable RAISE when the drive is configured at the factory.
OCZ V3 60GB drives have disabled RAISE.
OCZ V3 120GB & 240GB drives have RAISE enabled.
All of OCZ V2 drives have RAISE enabled.
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