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Author Topic: Mysterious short pause during playback Carsten Kurz Film God Posts: 4340 From: Cologne, NRW, Germany Registered: Aug 2009 posted 04-21-2012 05:46 PM                     Scott was not just referring to a hardware-raid controller, but a hardware-raid-controller with battery buffering. When the system shuts down unexpectedly, it can buffer the pending data transfer in memory and perform it on the next power-up. However, there are other strategies to recover from power outages even with software raid. Software RAID5 without battery buffering is in widerspread use on computer systems and RAID appliances nowadays. If they'd be prone to critical file system corruption the way Scott describes it, that whole business would be dead already. I don't know of any DCI server with hardware+battery buffered RAID5. A UPS is another quite useful (and cheap) investment not only to aid in file system consistency, but also for fast show-time recovery from power-outages. A UPS is standard with all Sony installations, with the Sony using RAID6+dedicated spare drive. But all other projectors can be retrofitted with a UPS as well. - Carsten  |  IP: Logged Scott Norwood Film God Posts: 8146 From: Boston, MA. USA (1774.21 miles northeast of Dallas) Registered: Jun 99 posted 04-21-2012 07:36 PM                        I realize that a DCI server can "get away" with software RAID 5 because it is mostly reading from the array, not writing to it, and mdadm and other software RAID mechanisms aren't as fragile as I may have made it sound. Still, I would not trust my own data to any software RAID variant other than level 1 or 1+0 (or maybe RAIDZ). Something like RAID 5 or RAID 6 really requires the aforementioned battery-backed hardware controller to be considered safe. And good backups are, of course, always essential.  |  IP: Logged Terrence Meiczinger Film Handler Posts: 45 From: Orono, Me, USA Registered: Dec 2008 posted 04-21-2012 08:36 PM                        I think there are misconceptions on the purpose of the battery backup on RAID controllers and that leads people to believe it is safer than software raid. The reason for battery backup is to allow the RAID controller to operate in a caching mode which increases performance. In this mode, data writes are cached on the controller. When the controller cache becomes full (or sometimes a period of time), it writes the data out to the drives. The issue in this scenario is that if the power failure occurs and data is still cached, it will be lost. Hence, battery backup. Although, many controllers now use flash backed cache and eliminate the battery. Regardless of whether you use hardware or software, a power failure during a drive write can cause a mismatch in parity. Both will detect this and resync. The difference is that a hardware controller can typically resync faster and sooner than software RAID upon reboot. I don't see hardware RAID being any safer than a good software implementation.  |  IP: Logged Eric Robinson Jedi Master Film Handler Posts: 538 From: Santa Rosa, CA Registered: Jan 2005 posted 04-22-2012 10:33 PM                     UPS systems seem to be held in high regard; however, even if a UPS system sustains power to a server during a power outage, it will eventually drain its reserves and the server will abruptly loose power just as it would without a UPS. So, it would seem that the value of the UPS would be that it could notify the server to shutdown gracefully; although, all of the UPS installs I have seen are not integrated to communicate with the server...so what good are they?  |  IP: Logged Brad Miller Administrator Posts: 17775 From: Plano, TX (36.2 miles NW of Rockwall) Registered: May 99 posted 04-23-2012 02:15 AM                     Assuming that a GOOD UPS is installed and not some piece of cheap junk, it will keep the system running for quite some time, typically more than adequate enough for power to be restored to the building.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 04-23-2012 06:24 AM                     The vast majority of power interruptions are in the split-second to a second or two. For longer periods then yes one would need to shut down the system prior to the battery dying...but even if it died via battery...it would be a clean stop. Normally if there is a power interruption via the power company, there is a surge/spike associated with it and the sensitive equipment will be shielded from that so it functions as an uber surge/spike arrestor too since the power is fed via the UPS directly, not the power grid (depending on the model of UPS and style). Better automation designs also will, upon sensing a power loss of greater than say a second, will stop the show in progress too since the sound/lighting will likely go away (plus the picture because very few put a UPS on the xenon lamp supply). Having a UPS for the automation allows it to do these functions. Most of the TMS/LMS servers I've seen do, in fact, have a means for the UPS to shut down the TMS/LMS gracefully before the battery completely dies. -Steve  |  IP: Logged

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