BackupPC-users

Re: [BackupPC-users] usb slow for random access? (was Re: Using rsync for blockdevice-level synchronisation of BackupPC pools)

2009-09-11 14:21:09
Subject: Re: [BackupPC-users] usb slow for random access? (was Re: Using rsync for blockdevice-level synchronisation of BackupPC pools)
From: Les Mikesell <lesmikesell AT gmail DOT com>
To: "General list for user discussion, questions and support" <backuppc-users AT lists.sourceforge DOT net>
Date: Fri, 11 Sep 2009 13:18:03 -0500
Dan Pritts wrote:
> On Wed, Sep 09, 2009 at 11:46:41AM +0200, Tino Schwarze wrote:
>> I'd say: Replace that USB 2.0 disk by something else like something
>> connected via Firewire or eSATA. USB 2.0 is very, very slow, especially
>> for random access.
> 
> Hi Tino,
> 
> do you have empirical results that show this?  
> 
> Not having tested it myself, that is exactly the opposite of what i
> would expect.
> 
> random access times are dominated primarily by disk head seek time,
> which is gonna be the same no matter what the transport to the drive is.
> So the slower transport won't matter nearly as much with random I/O as
> it will with sequential.
> 
> SATA or SAS/SCSI with command queueing should have better random access
> performance than anything without command queueing.  However, I don't
> believe firewire has command queueing support, which would suggest that
> this isn't what you're thinking of.  

I think USB has a bit more CPU overhead than firewire so firewire would 
give somewhat better throughput.   But eSATA or a hot-swap internal bay 
for a bare SATA drive would be even better.

-- 
   Les Mikesell
    lesmikesell AT gmail DOT com

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