3 ms·

I still don't see why this is such a big deal. Let's say everyone agrees on a standard and guarantees to make fsync() send data to a disk. Does this guarantee e

by zzzcpan 11y ago

I still don't see why this is such a big deal. Let's say everyone agrees on a standard and guarantees to make fsync() send data to a disk. Does this guarantee even worth anything? Will every disk suddenly disable write cache on itself by default? Who is going to sacrifice performance and make it a default? Even if somebody is going to do it, will disks suddenly become bug-free, 100% reliable and indestructible?

fulafel 11y ago
fsync works fine with on disk write caches (if the OS so chooses, ie not OS X). It's all specified in SATA and SCSI. Yes you can have bugs and lying devices, but reputable stuff is generally fine.
- mtanski 11y ago
  Many consumer drives tend to omit this feature (or lie about it) because all anybody looks at is size and iops. Nobody sells more consumer drives by advertising that the writeback cache on the drive respects flush commands (and barriers).
  - fulafel 11y ago
    Which current or recent sata/scsi drive omits or lies about cache flush commands? Leaving FUA unimplemented is fine. Bottom of barrel flash sticks probably do lie, and some IDE era PC drives did, but major disk vendors are pretty sensitive about their reputations wrt data integrity now.
    - mtanski 11y ago
      A few years ago some of the intel SSD drives has issues with this. http://www.evanjones.ca/intel-ssd-durability.html http://www.evanjones.ca/intel-ssd-durability.html Drive was advertising FUA but it didn't actually implement it (or implemented it incorrectly). Then there were drives that were storing things in cache and reporting as written but didn't actually have capacitors to write out the data in case of power failure. http://lkcl.net/reports/ssd_analysis.html http://lkcl.net/reports/ssd_analysis.html , also the paper from FAST13. I think in 2016 the situation looks much better.
      - deleted 11y ago
        [deleted]

3 ms·

I still don't see why this is such a big deal. Let's say everyone agrees on a standard and guarantees to make fsync() send data to a disk. Does this guarantee e

by zzzcpan 11y ago

fulafel 11y ago
fsync works fine with on disk write caches (if the OS so chooses, ie not OS X). It's all specified in SATA and SCSI. Yes you can have bugs and lying devices, but reputable stuff is generally fine.
- mtanski 11y ago
  Many consumer drives tend to omit this feature (or lie about it) because all anybody looks at is size and iops. Nobody sells more consumer drives by advertising that the writeback cache on the drive respects flush commands (and barriers).
  - fulafel 11y ago
    Which current or recent sata/scsi drive omits or lies about cache flush commands? Leaving FUA unimplemented is fine. Bottom of barrel flash sticks probably do lie, and some IDE era PC drives did, but major disk vendors are pretty sensitive about their reputations wrt data integrity now.
    - mtanski 11y ago
      A few years ago some of the intel SSD drives has issues with this. http://www.evanjones.ca/intel-ssd-durability.html http://www.evanjones.ca/intel-ssd-durability.html Drive was advertising FUA but it didn't actually implement it (or implemented it incorrectly). Then there were drives that were storing things in cache and reporting as written but didn't actually have capacitors to write out the data in case of power failure. http://lkcl.net/reports/ssd_analysis.html http://lkcl.net/reports/ssd_analysis.html , also the paper from FAST13. I think in 2016 the situation looks much better.
      - deleted 11y ago
        [deleted]