Ron Mayer wrote: > Bruce Momjian wrote: > > Agreed, thought I thought the problem was that SSDs lie about their > > cache flush like SATA drives do, or is there something I am missing? > > There's exactly one case I can find[1] where this century's IDE > drives lied more than any other drive with a cache: > > Under 120GB Maxtor drives from late 2003 to early 2004. > > and it's apparently been worked around for years. > > Those drives claimed to support the "FLUSH_CACHE_EXT" feature (IDE > command 0xEA), but did not support sending 48-bit commands which > was needed to send the cache flushing command. > > And for that case a workaround for Linux was quickly identified by > checking for *both* the support for 48-bit commands and support for the > flush cache extension[2]. > > > Beyond those 2004 drive + 2003 kernel systems, I think most the rest > of such reports have been various misfeatures in some of Linux's > filesystems (like EXT3 that only wants to send drives cache-flushing > commands when inode change[3]) and linux software raid misfeatures.... > > ...and ISTM those would affect SSDs the same way they'd affect SATA drives. I think the point is not that drives lie about their write-back and write-through behavior, but rather that many SATA/IDE drives default to write-back, and not write-through, and many administrators an file systems are not aware of this behavior. -- Bruce Momjian <bruce@xxxxxxxxxx> http://momjian.us EnterpriseDB http://enterprisedb.com PG East: http://www.enterprisedb.com/community/nav-pg-east-2010.do + If your life is a hard drive, Christ can be your backup. + -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
