RE: Transfer Rates - Dantz Help?
Matt, if you think you're actually getting 4:1 real world compression out of a modem, I suggest you read some of the research on the subject. Compression is highly variable, depends on the data, and 4:1 is rarely achieved. What's more it induces considerable latency, often exceeding the value of the compression. The irony is that lower compression rates take less processing time and power than attempting to achiieve higher compression. Now latency isn't as big an issue for backup as it is for a highly dynamic, realtime application like modems support. However, the data pipe is vastly greater. Fast ethernet has a thousand times the bandwidth of a 56 k modem, about twice the uncompressed streaming rate of a 7000 series DLT drive. What does this all mean? Basically if you have a fast ethernet connection with no routers inbetween the host and station the hardware should support uncompressed streaming to tape. Compressed files will probably not quite stream, but to do software compression at the clients would require very fast clients; it's one of the many specialized tasks that is easier to do in hardware - at the tape drive. You're most likely constrained by disk access speed anyway. BTW, this is an old question, hardly unique to Dantz. Client compression has been tried, and can be a useful tool under some circumstances, but it usually causes as many problems as it solves. And you're right about aquiring vs creating compression technologies. It usually doesn't make sense to reinvent that particular wheel. Other methods of improving data feeds to the tape drive include intelligent backup (something Retrospect is very good at) and multiplexing data sources. This last option has it's proponents, but tends to be rather cranky in practice - and restores are very slow. -Original Message- From: matt barkdull To: retro-talk Sent: 2/26/01 10:52 AM Subject: RE: Transfer Rates - Dantz Help? A month or so ago I wrote a rant about how Dantz should work with Alladin and come up with a better compression scheme. I know that the on-fly compression is difficult to maintain speed, but it seems like better than 2:1 should be possible. I'm not much of a wiz at all with compression, however I see modems getting v.42bis (4:1) on the fly, it seems like a little work and this should be possible for client and server as well. Yes, I know that advertised and what you really get are totally different, but all I know is that if something is advertised at 4:1, it will be more likely to get at least 2:1 that 2:1 is likely to. Alladin is cross platform. Dantz covers the same platforms. Yes, most people use hardware compression, but this is mostly because the hardware and software compression are likely to get the same results. Why would anyone want to write their own compression? I mean, a license deal from Alladin, who's been doing it since the early days of Mac, would seem like it would be far more cost effective. -- -- To subscribe:[EMAIL PROTECTED] To unsubscribe: [EMAIL PROTECTED] Archives:http://list.working-dogs.com/lists/retro-talk/ Search: http://www.mail-archive.com/retro-talk%40latchkey.com/ For urgent issues, please contact Dantz technical support directly at [EMAIL PROTECTED] or 925.253.3050.
Re: Transfer Rates - Dantz Help?
Can someone at Dantz answer this please? Thanks David Ross wrote: I know this has been answered here before but I can't find it in any of the messages I've saved. Is the data rate shown in the real time backup progress window the rate at which data, compressed or not, is going to the drive or is it the rate at which the data is being lifted off the source disk? Or in other words is it based on the 100mb of the source file or the maybe 20mb after software compression? -- -- To subscribe:[EMAIL PROTECTED] To unsubscribe: [EMAIL PROTECTED] Archives:http://list.working-dogs.com/lists/retro-talk/ Search: http://www.mail-archive.com/retro-talk%40latchkey.com/ For urgent issues, please contact Dantz technical support directly at [EMAIL PROTECTED] or 925.253.3050.
Re: Transfer Rates - Dantz Help?
Don't quote me on this, but I think it is the source. That is, the amount of data read from the source drive, before compression. Which would make the most sense because that is the real number that people need to look at. Matt Can someone at Dantz answer this please? Thanks David Ross wrote: I know this has been answered here before but I can't find it in any of the messages I've saved. Is the data rate shown in the real time backup progress window the rate at which data, compressed or not, is going to the drive or is it the rate at which the data is being lifted off the source disk? Or in other words is it based on the 100mb of the source file or the maybe 20mb after software compression? -- -- To subscribe:[EMAIL PROTECTED] To unsubscribe: [EMAIL PROTECTED] Archives:http://list.working-dogs.com/lists/retro-talk/ Search: http://www.mail-archive.com/retro-talk%40latchkey.com/ For urgent issues, please contact Dantz technical support directly at [EMAIL PROTECTED] or 925.253.3050. -- -- To subscribe:[EMAIL PROTECTED] To unsubscribe: [EMAIL PROTECTED] Archives:http://list.working-dogs.com/lists/retro-talk/ Search: http://www.mail-archive.com/retro-talk%40latchkey.com/ For urgent issues, please contact Dantz technical support directly at [EMAIL PROTECTED] or 925.253.3050.
Re: Transfer Rates - Dantz Help?
The performance is based on the raw number of MB transferred to the backup device from the source volume. BEFORE software compression? I ask since as I understand it remote clients compress before shipping to the Retrospect module that doing the writing to the device. Thanks -- -- To subscribe:[EMAIL PROTECTED] To unsubscribe: [EMAIL PROTECTED] Archives:http://list.working-dogs.com/lists/retro-talk/ Search: http://www.mail-archive.com/retro-talk%40latchkey.com/ For urgent issues, please contact Dantz technical support directly at [EMAIL PROTECTED] or 925.253.3050.
Re: Transfer Rates - Dantz Help?
Yes, these are numbers before compression. The client does not compress data before sending it across the network. Further, Retrospect has no way to know what kinds of compression you're getting if you're using hardware compression. All number reported reflect the raw data being copied from the source. Regards, Irena Solomon Dantz Technical Support 925.253.3050 Try our new Searchable Knowledgebase at: http://partners.dantz.com:591/faq/ From: David Ross [EMAIL PROTECTED] Subject: Re: Transfer Rates - Dantz Help? The performance is based on the raw number of MB transferred to the backup device from the source volume. BEFORE software compression? I ask since as I understand it remote clients compress before shipping to the Retrospect module that doing the writing to the device. Thanks -- -- To subscribe:[EMAIL PROTECTED] To unsubscribe: [EMAIL PROTECTED] Archives:http://list.working-dogs.com/lists/retro-talk/ Search: http://www.mail-archive.com/retro-talk%40latchkey.com/ For urgent issues, please contact Dantz technical support directly at [EMAIL PROTECTED] or 925.253.3050.
