Tuesday July 12, 2005 Weblog
Tuesday July 12, 2005 A bit of SVM history (answering Francis' question)
I finally realized I should check for comments on my blog and found that Francis Liu asked the following question back on June 19th (with regards to my RAID 0+1 vs. RAID 1+0 and SVM blog):
One question, is the desciprion true for all versions of DiskSuite. Or is it only true for SVM (ie Solaris 10 or OpenSolaris)? I've seen documents that say that this sort of thing only applies to SDS 4.2.1 with patches and later.
While I started working with DiskSuite for the 4.2.1 release, I know that the convoluted mirror/stripe interaction dates back to well before then. I arrived on the SDS scene in 1999 when development was ramping back up after a period of inactivity. Several years earlier Sun had closed down the Rocky Mountain Technical Center (RMTC) in Colorado Springs. One of the casualties was the SDS development group. At the time upper management seemed to think that continued development of SDS wasn't a good investment and so while the product continued to be available there wasn't ongoing development. This decision was reversed some time later, but as the vast majority of the RMTC engineers had left Sun an SDS development group needed to be restarted mostly from scratch.
I know that current mirror/concat/stripe paradigm existed in the SDS 4.1 release (which dates to before the dissolution of RMTC) and I suspect its roots go back much further than that. The mirror and concat/stripe devices are so intertwined that my guess is that they were designed together in the very early days of the code base that eventually became SVM. My understanding is that mirror/concat/stripe devices are the earliest ODS/SDS/SVM devices, followed later by trans devices (since discontinued in favor of logging ufs) and RAID5. Soft Partitions are a relatively late addition, being made after I joined the SDS team.
A bit more SVM history: The earliest references I've seen to the product refer to it as ODS (for "Online: DiskSuite"). At some point the name was changed to SDS ("Solstice DiskSuite"). In both cases the volume manager was an "add on" product rather than being built into Solaris. One of the major disadvantages of this was that upgrade didn't understand SDS metadevices, so if your system had a mirrored root you had to eliminate the mirror before upgrading and then recreate the root mirror after the upgrade. The decision was made to integrate SDS into base Solaris for the S9 release and the initial name chosen was Solaris Logical Volume Manager (SLVM, pronounced "sliv-em"). Before S9 actually shipped the decision was made to shorten the name to Solaris Volume Manager (SVM, or "siv-em"). While all the release docs were changed to show SVM instead of SLVM, a few references to SLVM persisted in error messages and comments in the code for some time after the S9 release before finally being eradicated.
I've heard that original base code for ODS/SDS/SVM was bought by Sun from another company back in the late eighties or early nineties but have never seen any confirmation of that.
Solaris ( Jul 12 2005, 05:02:09 AM PDT ) Permalink Comments [0]
