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(?) The Answer Guy (!)

By James T. Dennis, tag@lists.linuxgazette.net
LinuxCare, http://www.linuxcare.com/

(?) Arco Duplidisk: Disk Mirroring

From Randy Kerr on Tue, 08 Jun 1999

Hi Jim,

Not quite sure how to post a question to the 'Answer Guy' and this seems to be the only option.

(!) One of these days we should clarify that. The address tag@lists.linuxgazette.net> should work, and, of course my home/personal address at starshine.org (deprecated).

(?) I was wondering if you have had any experience or know of anyone using Arco's DupliDisk for mirroring IDE drives. Wanted to know something about reliability, ease of installation, etc. Specifically, if a hard disk must be cloned prior to linking to its mate, or if the card mirrors the entire drive upon installation.

Thanks a lot.
Randy Kerr

(!) I don't have any experience with these controllers.
However it should work. According to their FAQ (http://www.arcoide.com/faq.htm):
Q : Does the DupliDisk support Windows 95, 98 and NT?
A : Yes, the DupliDisk is a total hardware solution and will work with any operating system--Windows 3.x, 95, 98 and NT, UNIX, LINUX, BSDI, FreeBSD, OS/2, Novell, Solaris386--without the use of
I have no idea regarding ease of use, reliability or any of that. A web search on the phrase "Arco Duplidisk" generates almost a 100 hits at Yahoo! including reviews in Computerist Magazine (http://www.p3p.com), VAR Business (http://www.varbusiness.com), Telephony World (http://www.telephonyworld.com), PC Today (http://www.pctoday.com) Medicine News (http://www.medicine-news.com/articles/computer)
Here are pointers to those reviews directly though I'm no judge of their accuracy or value:
Arco Announces New IDE Backup Device DupliDisk Makes Disk Mirroring an Affordable Option
Arco Will Back You Up - VARBUSINESS - December 1996
Arco Announces New IDE Backup Device DupliDisk Makes Disk Mirroring an Affordable Option
ARCO Computer,DupliDisk,medicine-news.com, Press Releases computer hard- and software,
PC Today's Hard-Hitting Product Reviews
In any event I'm not sure that the ~$200 you'd spend on one of these would really net you much advantage over Linux built-in md (multi-device) drivers (which implement striping, mirroring and RAID 5 through software).
These devices don't do give any performance advantage over a single disk drive (mentioned in their FAQ). Even the Linux software driver gives some performance edge over single disk (by interleaving read and write requests among the available drives and resynching the devices asynchronously through its caching mechanisms).
You should also consider the nature of the risks which the Duplidisk addresses vs. the actual risk profiles that are present. Duplidisk only protects you from a single drive failure (per controller). It doesn't address accidental deletion, damage due to software bugs (data corruption, etc) or deliberate sabotage due to failures in your security measures (including crackers, trojans, viruses, etc).
Drive failure is currently one of the less common causes of data losss under Linux (although the rate of damage caused by PC virus infection are probably even lower than disk failure under Linux).
Overall, I think you're much better served by using an extra hard drive (which you'd connect to Duplidisk) and just perform nightly snapshots to it using 'cp -pax' and or 'cpio -p' or 'tar cf ...' piped into a 'tar xf ...' The "snapshot" method protects against several different threats --- particularly that of accidental deletion; which is the most common cause of data loss. (If you have a 'cron' job which makes your snapshots in the middle of the night you'll usually have a half a day or so to realize that you've accidentally removed or damaged some of them).
Personally I think that's a better way of spending your money. (Heck, you can use the extra two hundred bucks to put in a third drive --- and use a combination of md/RAID-1 --- mirroring across a pair of drives and using the third for snapshots).

Copyright © 1999, James T. Dennis
Published in The Linux Gazette Issue 43 July 1999
HTML transformation by Heather Stern of Starshine Techinical Services, http://www.starshine.org/

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