6 ms·

Do these drives feature power-loss capacitors? I'm still wondering why most manufacturers think it's okay to offer SSDs that lose data on power loss (!!)

nik736 9y ago
What are you wondering about? They can squeeze more money out of businesses because it is sold as enterprise feature.
nine_k 9y ago
I really wonder why a $10 capacitor add-on (a capacitor, a diode, two connectors) plugged in between main board power supply and a disk power receptacle is not a common item. Or maybe it is, but I have no idea?
- marshray 9y ago
  A common minimum voltage requirement for the nominal +5V supply is 4.5 V. Let's assume a voltage below that won't damage the drive, but it won't operate. The diode is going to drop 0.6V, leaving you with only 4.4 V max for the drive. Then the capacitor is going to immediately start dropping in voltage as soon as you start pulling the stored energy out of it. So, in practice, to do a quality job of this it will probably need a DC-DC converter. These aren't necessarily expensive, but definitely more complicated than the old diode trick.
  - nine_k 9y ago
    This makes sense! OTOH low-drop diodes do exist [1], and the drive likely needs just a (small) fraction of a second to flush the caches; it's SSD, not need to wait for the disk to rotate to the right position or move heads. I suppose the power loss signal from the controller still propagates, even if the computer's PSU plug is just yanked out of socket. [1]: https://electronics.stackexchange.com/a/282471/9909 https://electronics.stackexchange.com/a/282471/9909
    - jotux 9y ago
      I implemented a power-loss circuit on a custom USB memory device (battery-backed LPDDR disks) and used something similar: the MAX40200[1]. [1]https://www.maximintegrated.com/en/products/analog/amplifiers/MAX40200.html https://www.maximintegrated.com/en/products/analog/amplifier...
    - londons_explore 9y ago
      The caches on some SSD's can be multiple gigabytes. They also frequently cache data which can be difficult (slow) to write, for example a single modified 4kb page which is part of a large unmodified area. Completing that write would involve reading the original data, erasing the entire erase-block, and rewriting the new data. SSD's with built in power loss prevention typically reserve an area on the SSD which is pre-erased ready to dump the contents of the cache into. Then on powerup, they reload the cache and properly flush the data to the actual place it's supposed to be.
  - jotux 9y ago
    You also need to limit in-rush current without dropping that voltage and account for capacitor degradation over the life of the device.
- pkaye 9y ago
  I worked on SSD power loss implementation in the past. You also need a signal into the controller indicating power failed. At this point the controller will minimally stop all less critical tasks, prioritize the buffered user data to be written and make sure the FFS is in consistent state for recovery.
- 21 9y ago
  Desktop power supplies already have that, they can keep the power on for 50-100 ms or so, and they do notify the OS about the imminent power loss. I'm not sure what OSes do with that.
  - gsich 9y ago
    How do they notify?
    - londons_explore 9y ago
      ATX power supplies have a PWR_OK pin, which goes low when power is lost. Most motherboards don't report that to the OS though, instead they simply reset all the hardware. To be fair, it's probably preferable to reset stuff than to operate when the power supply isn't healthy, since that will lead to a lot of weird undefined behaviour.
rhn_mk1 9y ago
I wish reviews started taking reliability into account. The only report on power loss effects on actual hardware I could find is from 2014 [0]. http://lkcl.net/reports/ssd_analysis.html http://lkcl.net/reports/ssd_analysis.html
- nh2 9y ago
  That article said back in the day > Right now, there is only one reliable SSD manufacturer: Intel. Indeed I find it very hard to figure out for other vendors whether they have power loss protection or not. Intel makes this easy to check: Each drive has a YES/NO for "Enhanced Power Loss Data Protection" which is described as > ... prepares the SSD for unexpected system power loss by minimizing data in transition in temporary buffers, and uses on-board power-loss protection capacitance to provide enough energy for the SSD firmware to move data from the transfer buffer and other temporary buffers to the NAND, thus protecting system and user data. They also have a list showing all Intel SSDs that have this feature: https://ark.intel.com/Search/FeatureFilter?productType=solidstatedrives&EPLDP=true https://ark.intel.com/Search/FeatureFilter?productType=solid... Would be nice if other vendors had that too.
stefan_ 9y ago
So what happens when you have "power-loss capacitors"? Since these things are limited the drive races to empty its buffers onto the SSD and then shuts down. It does not ask the host "are you done writing", so now instead you lose whatever the host had in its buffers. The host is gone anyway when the drive loses power. No. Data loss protection needs to be built into the software itself, fixing that on the SSD level doesn't make a lot of sense. If anything, you install a UPS, and then of course you don't need to pay extra for SSD capacitors because the whole system keeps running through power loss and shuts down gracefully.
- whitepoplar 9y ago
  Power-loss capacitors are needed because without them, flush commands issued by the OS return bogus values. Write confirmations are meaningless if the data isn't actually written to disk.
  - stefan_ 9y ago
    Doesn't software like databases that care about this already assume the OS flush return values are bogus? And it still doesn't solve the problem of the host buffers disappearing. What's the scenario, the host experiences a power-loss, but was somehow anticipating it and managed to stop writing to the SSD?
    - makmanalp 9y ago
      > Doesn't software like databases that care about this already assume the OS flush return values are bogus? Unsure of this (I would assume "it depends" and "probably not" because how else could it possibly know that anything is written to durable storage ever ever) but the idea is that if it didn't have to assume that life would be a lot easier. > What's the scenario, the host experiences a power-loss, but was somehow anticipating it and managed to stop writing to the SSD? If I understood your question correctly, databases and similar stuff write data in a way to try to solve exactly this problem, with write-ahead logs and such where you first write quickly and inexpensively to the log and then write to the database.
    - 9y ago
pkaye 9y ago
I've worked on PLP implementations in the past. Mostly it was the added cost of capacitors. Also things like laptops don't really need them since they have batteries and will shut down gracefully when battery is running low. The capacitors needs to be reliable, small form factor and hold enough charge to keep the controller, DRAM and NAND powered for a minimum of 15-30ms. 10 years ago what was available was not so great but now the options are much better.
- whitepoplar 9y ago
  Given your work with PLP, which family of SSDs would you recommend most?
  - pkaye 9y ago
    I personally use the Samsung PRO SSDs myself these days. I don't go with the latest models because the older NAND technology tends to be more reliable. Also you want a company with many product cycles so that the firmware has time to mature. Just too many edge cases in SSD firmware to catch them in one go.
    - AnonymousR 9y ago
      Well, speaking of firmware, the current state of Samsung's SSD firmware is incredibly poor. I jumped ship from SATAs to M.2 a month ago with a new computer and to quickly sum up the situation with Samsung 960 Pro from own experience and hundred page long threads on official product forum: - last published firmware on website is 2 (don't know the long number now, writing from phone) - a version 3 was released, system freezing started occurring in some cases and some people even ended up with bricked drives (in relation to eDrive IIRC) - bricked drives could be reportedly used again after PSID revert, but Samsung consistently refuses to release the tool (other manufacturers do and the tool is also useful for recovering drive with lost OPAL password) - firmware 4 reportedly exists, which can be obtained through Magician (Samsung's tool for SSD) and should solve problems from version 3. Conflicting reports on performance. The craziest stuff is that: - Magician will now tell you there is a new firmware for your drive, but it won't tell you with which version is it going to "enrich" your shiny new drive. Will I get 3? Or 4? Especially when only 2 is posted on the Samsung's page! - firmware changelogs are kept secred, just install this for no reason - no downgrades are possible Worse than X25-M password bug. You have to be scavenging official forums for information that should be posted with the firmware and be cursing at/begging moderators to reveal some more. Ah and reportedly there is some mysterious incompatibility with major BIOS vendors in regard to eDrive. No, they won't tell what the bug is, nor on what boards. Also, custom OPAL PBAs (image flashed to special unlocked area on disk for booting with disk locked down) don't boot in current desktop boards. Might be non-Samsung issue, maybe the one mentioned above. How does this stuff work together at all?
berg01 9y ago
I guess Samsung is just not at their top of their game in terms of pushing differentiated product lines for their M.2 SSDs. Perhaps (or perhaps not) they should learn from Taiwanese companies. They would jump on this opportunity to sell a premium edition for lots of extra margin profit. Have a look at this wonderful marketing page for a Gigabyte Z370 motherboard: https://www.gigabyte.com/us/Motherboard/Z370-AORUS-Gaming-7-rev-10 https://www.gigabyte.com/us/Motherboard/Z370-AORUS-Gaming-7-... It's the most over-the-top glorious thing I've ever seen. Make sure you expand a couple of the sections.
TwoNineFive 9y ago
No, and for numerous reasons. Capacitors are relatively large and bulky. The specifications for SSD size doesn't leave a lot of room, and the type of surface mount electrostatic capacitors which would be needed are both expensive and take up a lot of space. Even in the enterprise market, M2 form factor SSDs rarely have these capacitors, because they don't really help. They are more common on PCIE-card devices. The on-disk/flash format that these drives use has a journaling system much like modern filesystems do, so they know if blocks were not fully written. This feature alone almost completely negates any need for I have committed patches and code to UBIFS and I am very familiar with how modern flash filesystems work at the hardware level. Backup caps are just not really needed. PS: The double exclamation point and whiney-blamey statement really added to your immature hyperbolicity.

nik736 9y ago

What are you wondering about? They can squeeze more money out of businesses because it is sold as enterprise feature.

nine_k 9y ago

I really wonder why a $10 capacitor add-on (a capacitor, a diode, two connectors) plugged in between main board power supply and a disk power receptacle is not a common item. Or maybe it is, but I have no idea?

marshray 9y ago
A common minimum voltage requirement for the nominal +5V supply is 4.5 V. Let's assume a voltage below that won't damage the drive, but it won't operate. The diode is going to drop 0.6V, leaving you with only 4.4 V max for the drive. Then the capacitor is going to immediately start dropping in voltage as soon as you start pulling the stored energy out of it. So, in practice, to do a quality job of this it will probably need a DC-DC converter. These aren't necessarily expensive, but definitely more complicated than the old diode trick.
- nine_k 9y ago
  This makes sense! OTOH low-drop diodes do exist [1], and the drive likely needs just a (small) fraction of a second to flush the caches; it's SSD, not need to wait for the disk to rotate to the right position or move heads. I suppose the power loss signal from the controller still propagates, even if the computer's PSU plug is just yanked out of socket. [1]: https://electronics.stackexchange.com/a/282471/9909 https://electronics.stackexchange.com/a/282471/9909
  - jotux 9y ago
    I implemented a power-loss circuit on a custom USB memory device (battery-backed LPDDR disks) and used something similar: the MAX40200[1]. [1]https://www.maximintegrated.com/en/products/analog/amplifiers/MAX40200.html https://www.maximintegrated.com/en/products/analog/amplifier...
  - londons_explore 9y ago
    The caches on some SSD's can be multiple gigabytes. They also frequently cache data which can be difficult (slow) to write, for example a single modified 4kb page which is part of a large unmodified area. Completing that write would involve reading the original data, erasing the entire erase-block, and rewriting the new data. SSD's with built in power loss prevention typically reserve an area on the SSD which is pre-erased ready to dump the contents of the cache into. Then on powerup, they reload the cache and properly flush the data to the actual place it's supposed to be.
- jotux 9y ago
  You also need to limit in-rush current without dropping that voltage and account for capacitor degradation over the life of the device.
pkaye 9y ago
I worked on SSD power loss implementation in the past. You also need a signal into the controller indicating power failed. At this point the controller will minimally stop all less critical tasks, prioritize the buffered user data to be written and make sure the FFS is in consistent state for recovery.
21 9y ago
Desktop power supplies already have that, they can keep the power on for 50-100 ms or so, and they do notify the OS about the imminent power loss. I'm not sure what OSes do with that.
- gsich 9y ago
  How do they notify?
  - londons_explore 9y ago
    ATX power supplies have a PWR_OK pin, which goes low when power is lost. Most motherboards don't report that to the OS though, instead they simply reset all the hardware. To be fair, it's probably preferable to reset stuff than to operate when the power supply isn't healthy, since that will lead to a lot of weird undefined behaviour.

rhn_mk1 9y ago

I wish reviews started taking reliability into account. The only report on power loss effects on actual hardware I could find is from 2014 [0]. http://lkcl.net/reports/ssd_analysis.html http://lkcl.net/reports/ssd_analysis.html

nh2 9y ago
That article said back in the day > Right now, there is only one reliable SSD manufacturer: Intel. Indeed I find it very hard to figure out for other vendors whether they have power loss protection or not. Intel makes this easy to check: Each drive has a YES/NO for "Enhanced Power Loss Data Protection" which is described as > ... prepares the SSD for unexpected system power loss by minimizing data in transition in temporary buffers, and uses on-board power-loss protection capacitance to provide enough energy for the SSD firmware to move data from the transfer buffer and other temporary buffers to the NAND, thus protecting system and user data. They also have a list showing all Intel SSDs that have this feature: https://ark.intel.com/Search/FeatureFilter?productType=solidstatedrives&EPLDP=true https://ark.intel.com/Search/FeatureFilter?productType=solid... Would be nice if other vendors had that too.

stefan_ 9y ago

So what happens when you have "power-loss capacitors"? Since these things are limited the drive races to empty its buffers onto the SSD and then shuts down. It does not ask the host "are you done writing", so now instead you lose whatever the host had in its buffers. The host is gone anyway when the drive loses power. No. Data loss protection needs to be built into the software itself, fixing that on the SSD level doesn't make a lot of sense. If anything, you install a UPS, and then of course you don't need to pay extra for SSD capacitors because the whole system keeps running through power loss and shuts down gracefully.

whitepoplar 9y ago
Power-loss capacitors are needed because without them, flush commands issued by the OS return bogus values. Write confirmations are meaningless if the data isn't actually written to disk.
- stefan_ 9y ago
  Doesn't software like databases that care about this already assume the OS flush return values are bogus? And it still doesn't solve the problem of the host buffers disappearing. What's the scenario, the host experiences a power-loss, but was somehow anticipating it and managed to stop writing to the SSD?
  - makmanalp 9y ago
    > Doesn't software like databases that care about this already assume the OS flush return values are bogus? Unsure of this (I would assume "it depends" and "probably not" because how else could it possibly know that anything is written to durable storage ever ever) but the idea is that if it didn't have to assume that life would be a lot easier. > What's the scenario, the host experiences a power-loss, but was somehow anticipating it and managed to stop writing to the SSD? If I understood your question correctly, databases and similar stuff write data in a way to try to solve exactly this problem, with write-ahead logs and such where you first write quickly and inexpensively to the log and then write to the database.
  - 9y ago

pkaye 9y ago

I've worked on PLP implementations in the past. Mostly it was the added cost of capacitors. Also things like laptops don't really need them since they have batteries and will shut down gracefully when battery is running low. The capacitors needs to be reliable, small form factor and hold enough charge to keep the controller, DRAM and NAND powered for a minimum of 15-30ms. 10 years ago what was available was not so great but now the options are much better.

whitepoplar 9y ago
Given your work with PLP, which family of SSDs would you recommend most?
- pkaye 9y ago
  I personally use the Samsung PRO SSDs myself these days. I don't go with the latest models because the older NAND technology tends to be more reliable. Also you want a company with many product cycles so that the firmware has time to mature. Just too many edge cases in SSD firmware to catch them in one go.
  - AnonymousR 9y ago
    Well, speaking of firmware, the current state of Samsung's SSD firmware is incredibly poor. I jumped ship from SATAs to M.2 a month ago with a new computer and to quickly sum up the situation with Samsung 960 Pro from own experience and hundred page long threads on official product forum: - last published firmware on website is 2 (don't know the long number now, writing from phone) - a version 3 was released, system freezing started occurring in some cases and some people even ended up with bricked drives (in relation to eDrive IIRC) - bricked drives could be reportedly used again after PSID revert, but Samsung consistently refuses to release the tool (other manufacturers do and the tool is also useful for recovering drive with lost OPAL password) - firmware 4 reportedly exists, which can be obtained through Magician (Samsung's tool for SSD) and should solve problems from version 3. Conflicting reports on performance. The craziest stuff is that: - Magician will now tell you there is a new firmware for your drive, but it won't tell you with which version is it going to "enrich" your shiny new drive. Will I get 3? Or 4? Especially when only 2 is posted on the Samsung's page! - firmware changelogs are kept secred, just install this for no reason - no downgrades are possible Worse than X25-M password bug. You have to be scavenging official forums for information that should be posted with the firmware and be cursing at/begging moderators to reveal some more. Ah and reportedly there is some mysterious incompatibility with major BIOS vendors in regard to eDrive. No, they won't tell what the bug is, nor on what boards. Also, custom OPAL PBAs (image flashed to special unlocked area on disk for booting with disk locked down) don't boot in current desktop boards. Might be non-Samsung issue, maybe the one mentioned above. How does this stuff work together at all?

berg01 9y ago

I guess Samsung is just not at their top of their game in terms of pushing differentiated product lines for their M.2 SSDs. Perhaps (or perhaps not) they should learn from Taiwanese companies. They would jump on this opportunity to sell a premium edition for lots of extra margin profit. Have a look at this wonderful marketing page for a Gigabyte Z370 motherboard: https://www.gigabyte.com/us/Motherboard/Z370-AORUS-Gaming-7-rev-10 https://www.gigabyte.com/us/Motherboard/Z370-AORUS-Gaming-7-... It's the most over-the-top glorious thing I've ever seen. Make sure you expand a couple of the sections.

TwoNineFive 9y ago

No, and for numerous reasons. Capacitors are relatively large and bulky. The specifications for SSD size doesn't leave a lot of room, and the type of surface mount electrostatic capacitors which would be needed are both expensive and take up a lot of space. Even in the enterprise market, M2 form factor SSDs rarely have these capacitors, because they don't really help. They are more common on PCIE-card devices. The on-disk/flash format that these drives use has a journaling system much like modern filesystems do, so they know if blocks were not fully written. This feature alone almost completely negates any need for I have committed patches and code to UBIFS and I am very familiar with how modern flash filesystems work at the hardware level. Backup caps are just not really needed. PS: The double exclamation point and whiney-blamey statement really added to your immature hyperbolicity.