Re: [zfs-discuss] Re: ZFS questions (hybrid HDs)
On Jun 21, 2006, at 11:05, Anton B. Rang wrote: My guess from reading between the lines of the Samsung/Microsoft press release is that there is a mechanism for the operating system to pin particular blocks into the cache (e.g. to speed boot) and the rest of the cache is used for write buffering. (Using it as a read cache doesn't buy much compared to using the normal drive cache RAM for that, and might also contribute to wear, which is why read caching appears to be under OS control rather than automatic.) Actually, Microsoft has been posting a bit about this for the upcoming Vista release .. WinHEC '06 had a few interesting papers and it looks like Microsoft is going to be introducing SuperFetch, ReadyBoost, and ReadyDrive .. mentioned here: http://www.microsoft.com/whdc/system/sysperf/accelerator.mspx The ReadyDrive paper seems to outline their strategy on the industry Hybrid Drive push and the recent t13.org adoption of the ATA-ACS8 command set: http://www.microsoft.com/whdc/device/storage/hybrid.mspx It also looks like they're aiming at some sort of driver level PriorityIO scheme which should play nicely into lower level tiered hardware in an attempt for more intelligent read/write caching: http://www.microsoft.com/whdc/driver/priorityio.mspx --- .je ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
[zfs-discuss] Re: ZFS questions (hybrid HDs)
Actually, while Seagate's little white paper doesn't explicitly say so, the FLASH is used for a write cache and that provides one of the major benefits: Writes to the disk rarely need to spin up the motor. Probably 90+% of all writes to disk will fit into the cache in a typical laptop environment (no, compiling OpenSolaris isn't typical usage…). My guess from reading between the lines of the Samsung/Microsoft press release is that there is a mechanism for the operating system to pin particular blocks into the cache (e.g. to speed boot) and the rest of the cache is used for write buffering. (Using it as a read cache doesn't buy much compared to using the normal drive cache RAM for that, and might also contribute to wear, which is why read caching appears to be under OS control rather than automatic.) Incidentally, there's a nice overview of some algorithms (including file systems) optimized for the characteristics of FLASH memory that was published by ACM last year, for the curious (who happen to have access to either the online or their local library). http://doi.acm.org/10.1145/1089733.1089735 Anton This message posted from opensolaris.org ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
Re: [zfs-discuss] Re: ZFS questions (hybrid HDs)
Anton B. Rang wrote: Actually, while Seagate's little white paper doesn't explicitly say so, the FLASH is used for a write cache and that provides one of the major benefits: Writes to the disk rarely need to spin up the motor. Probably 90+% of all writes to disk will fit into the cache in a typical laptop environment (no, compiling OpenSolaris isn't typical usage…). On OpenSolaris laptops with enough RAM, we need to think about fitting mappings of libc, cron and all of its work into the buffer cache and then maybe the flash cache on the drive. Each time you execute a program, that's an atime uptdate of its file... I've known people to wear out laptop hard drives in a frighteningly short period of time because of the drive being spun up and down to service cron, sendmail queue runs, syslog messages... Darren ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
