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Performance Advice Part Duex


xazz

Question

If i have a DrivePool with 2x duplication, and it is serviced by two USB hard-drive towers. Naturally for best performance (only USB2 on the PC) it would be ideal to have all the originals on one tower and the dupes on the next. Is there an easy way to make it work that way?

 

Thanks

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Well, first, I don't recommend USB for long term connected storage.  It increases the likelihood of problems (such as the drives showing up "RAW").  eSATA would be better.  

 

For the sake of arguement, I'm going to assume "eSATA" here, or however. 

 

 

If you're using an internal beta version (2.2.0.7xx), then yes, you can do this.  It's a bit "complicated", but will work.

 

Specifically, create a pool for each tower.  So you have one pool for "Tower1" and another pool for "Tower2".

Then add each of these pools to a new pool.   You will have three pools because of this, but this would accomplish what you want.

You can then remove the drive letters of all of the drives, if you want.

 

And in this configuration, you would only want to duplicate on the "master pool" and not on the towers.  This way, one copy of the files exist on each tower, so that if one is disconnected, the file resides on the other tower, as well.

 

And you can find the latest version here:

http://dl.covecube.com/DrivePoolWindows/beta/download/StableBit.DrivePool_2.2.0.798_x64_BETA.exe

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Hi Christopher

 

Can you elaborate on your concerns regarding USB?

 

My whole purpose here was to make use of an existing HP PC and ten spare hard drives I have kicking around. The PC has a single esata port, which I doubt supports multiplying. Esata is simply not an option.

 

DrivePool was supposed to take all that hardware and make it into a useful file server (and it seems to be doing a good job of it). I don't really want to go back to the drawing board.

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IIRC, the USB specifications actually allow for spontaneous disconnects to occur.  Meaning that they are "fine".  That disconnect and then reconnect chime that you may have heard on some devices?  That's perfectly fine according the to the specifications.  Not so much for your data.

 

 

To be honest, a majority of people are going to be fine and not see an issue here.  But it's the possibility of issues that really bothers me.  Because if something does go wrong, it can damage the entire file system.

 

 

Worse, is that there are not many alternatives.  USB and eSATA are the main consumer interfaces for this.  eSATA is better, but as you mention, the lack of reliable or even properly implemented port multiplication makes it tricky at best.

 

 

 

The real problem isn't that the drives disconnect... but that there is nothing stopping, let alone compensating for the fact, that this can happen when you're writing data to the drive.

 

That means that the data can end up corrupt.  And if that data is the NTFS data structure, it can corrupt the entire file system, causing the drive to come up as "RAW".  And since the NTFS data structure gets modified every time you do anything on the drive really, the chance of this happening drops from "statistically unlikely" to a crapshoot.

 

 

Firewire, thunderbolt and other external interface aren't really much better, as the specifications are intentionally similar to USB.  And they're a lot less common....

 

 

The "best" interface for external storage is and will be SAS (Serial Attached SCSI). The problem is that this is enterprise grade stuff, and ... can quickly become expensive. 

For instance, this is a used controller card:

http://www.ebay.com/itm/68Y7354-IBM-LSI-SAS9212-4i-4e-6GBps-SAS-RAID-controller-PCI-e-/282094861972

 

This is ... rather cheap for it, as well. It supports both internal and external ports, but you can find versions that are just internal or just external.

But then you'd need a cable to add additional drives.

http://www.ebay.com/itm/Mini-SAS-26-P-SFF-8088-to-4-x-7-Pin-ESATA-External-Connector-Adapter-Cable-1M-/272292477058?epid=702517151&hash=item3f65e57882:g:2wcAAOSww5JZhjOd

 

And this can all quickly add up.  

 

 

The up side is that the LSI controls 60+ drives, minimum.  But again, this does come at a premium.

 

 

 

 

And I'm not really trying to scare you, but ... yes I am.  Data integrity is our first concern, which is why we recommend against USB for long term, online storage.  Using it as cold storage (write to it, unplug it) is just fine.  But keeping it up and on all the time, not so much.

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Thanks for the advice, Chris.

 

I've not (knowingly) seen NTFS corruption in my young life of some eighty hard drives, but given your history, you've probably seen a thousand times that, so I bow to your superior knowledge.

 

However, in my case, the data on the file server are all backups, so I can afford for them to be lost, even if - FSM forbid - both duplicates were corrupted simultaneously.

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Actually, the only annoyance with USB is that upon waking the devices take a few seconds to connect, so DP immediately emails me saying drives are missing, before emailing a few seconds later to report all is good (though it then remeasures the drive pool). It would be cool if there was an option like "Wait [___] seconds for missing drives to connect"

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There are actually a couple of settings that affect/do this.  however, I do believe that they're designed for the boot process and not "later on".

 

Specifically:

CoveFs_WaitForVolumesOnMount and CoveFs_WaitForVolumesOnMountMs 

These are default to "true" and "10000" (10 seconds), so this should be reasonable.

 

If you want, you can play with these settings here:

http://wiki.covecube.com/StableBit_DrivePool_2.x_Advanced_Settings

 

However, I wouldn't recommend setting this value too high. I don't think it will cause issues, but just in case...

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