<div>Please note that the article Anastasia reposted to the list is available on my company website <a href="http://www.dmevolve.com">www.dmevolve.com</a>, as well as other articles.</div><div><br></div><div>Anastasia has it wrong. If we're talking about support beams...</div>
<div><br></div><div>- RAID1 is making sure that every beam is at 50% capacity- you can lose half and your building won't fail.</div><div>- RAID0 is making sure that every beam is at 100% capacity- you can't lose a single beam without losing the building.</div>
<div><br></div><div>RAID0 takes individual files, divides them in half and splits them between drives, so if you lose one drive, you've lost all of your data. This doubles the write speed of the drives, which is why it is used at all, for specific purposes, which are _always_ stored elsewhere as well.</div>
<div><br></div>Striped is RAID 0 and like I said, increases the likelihood of data loss. Avoid it unless you know exactly why you want it. RAID 1 performs the exact function of making a SuperDuper or Carbon Copy Cloner mirror of your drive. Except that it does it better, as it is in real time. It _only_ protects you from disk failure, which is actually a rarity, unless your drive is very new or very old. In the latter case, it is a better idea to get a new drive, burn it in for two weeks, then migrate your data to it using CCC.<div>
<br></div><div>As for configuring a RAID. Disk Utility will wipe all drives when creating a RAID. However, it is possible to do it without wiping the drive using the diskutil command line application. Please do not do this unless you are comfortable with the commands and how to modify my examples to suit your needs. I am not teaching you how to get to the command line. If you don't already know, this is not the set of commands for you, as there is a very real chance to lose your data.</div>
<div><br></div><div>diskutil list (pay attention to the drivenumbers, which are listed as "disk#". Most Macs have a boot drive of disk0)</div><div>diskutil enableRAID mirror disk<drivenumber of main boot partition></div>
<div>diskutil repairMirror disk<drivenumber of main boot partition> disk<drivenumber of empty drive></div><div><br></div><div>The other thing is that the 1 TB drive will effectively become 500 GB, wasting the remaining space. I do not believe it is possible to partition part of a drive that is used in RAID, but could be wrong, as I _never_ use non-matching drives in RAID, like you are wanting to do here. Part of this is I/O. It is imperative that data is written to the two hard drives simultaneously, otherwise, data corrupting bottlenecks are possible. Since one hard drive is now responsible for two partitions, it no longer has 100% of it's time dedicated to maintaining the RAID.</div>
<div><br></div><div>Finally, the only way that I would consider doing a software based raid is if you have two internal drives, such as in a MacPro, XServe, or the new Mac Mini Server. DO NOT DO RAID OVER FIREWIRE. (Unless you are buying a RAID-based device like a Drobo, or the better performing Promise SmartStor DS4600, which house all drives internally.) If you have one drive internal, and the other over firewire and you pull the cord out, you are going to rebuild your RAID. Same with the power cord. It's just not a good idea, as you are increasing the likelihood of compromising your redundancy.</div>
<div>-- <br>Jon Thompson<br>Evolve<br><a href="http://www.dmevolve.com">www.dmevolve.com</a><br>
<br><br><div class="gmail_quote">On Sun, Nov 29, 2009 at 7:05 PM, AB <span dir="ltr"><<a href="mailto:anastasia_prittee@yahoo.com">anastasia_prittee@yahoo.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
<table cellspacing="0" cellpadding="0" border="0"><tbody><tr><td valign="top" style="font:inherit">As I understand it...<br>RAID Mirrored mirrors the contents and files of a single drive in the event that drive fails—see excerpts from the info Jon gave.<br>
RAID Stripped takes content and distributes it across multiple drives. Kind of like putting multiple support beams in. Each hard drive is a support beam and collectively behave as one unit. One of those drives failing won't necessarily have detrimental repercussions. I believe John Thompson gave a detailed description. Though I might be confused on this. <br>
<br>As far as erasing contents on the existing drive, I'm not sure and was wondering the same thing myself.<br><br>Here's what I saved for reference on what was mentioned before about RAID. I thought there was another detailed summary, Jon gave, but I this seems to be all I saved.<br>
<br>Jon Thompson wrote this on May 19, 2009:<br><br><div><b>1) A
good backup is a verifiable backup</b></div><div><br></div><div>If you are dumping info into <span>Time Machine</span>,
and you are _never_ pulling info back out of it and checking, how do
you know that the data is good? In the instance of the SideKick data,
this means that they would have known that the backup is good, and that
they could rely on it. Until you know that you can recover from it, you
cannot call it a good backup.</div><div><br></div><div><b>2) A good backup consists of many backups of the same data.</b></div><div><br></div><div>I
store three months of backups, and I consider that too little, but
don't dare increase my budget. If you are relying on all of your data
being on a single hard drive, what happens if there is a fire and both
your computer and backup is lost? If all of your backup is in one cloud
(Mozy) and that cloud bursts like the SideKick cloud did, you are
hosed. Now, if you have daily backups on a time machine volume, and a
weekly backup to Mozy, you are protected from either example. Mozy is
your <span style="border-bottom:1px dashed rgb(0, 102, 204)">offsite backup</span>, the time machine </div><div><br></div><div><b>3) Synchronization is not backup.</b></div><div><br></div><div>Synchronization
ensures that all of you data is the same between all instances that you
create. If you are syncing your address book on your mac with an
iPhone, you have two instances of the data, but they are tied together.
If you delete a contact on one (or a virus deletes all of them) that
deletion is transferred to your backup. I realize that there are ways
that the sync service tries to reduce the chance of this, but it is
still a possibility. However, an offline copy of your address book on a
USB thumb drive that is not plugged into your computer cannot not be
changed, at least until it is plugged in again. Dropbox is a
synchronization service.</div><div><br></div><div><b>4) RAID is not backup.</b></div><div><br></div><div>RAID
(except 0) is a way to protect from hard drive crashes. It does not
protect from application corruption, accidental deletion, or
intentional deletion. All of which are much more likely than hard drive
corruption during the majority of the life of a hard drive. RAID is
useful for server admins that deal with distributing data amongst many
hard drives, which actually is a great way to exponentially increase the likelihood of data loss due to <span style="background:transparent none repeat scroll 0% 0%">hard drive failure</span>.</div><div><br></div><div>RAID
0 offers no protection at all- in fact, it is will exponentially
increase your likelihood of data loss due to hard drive failure. Be
careful when purchasing large <span>external hard drive</span>, as they are sometimes two drives that are internally configured as RAID 0. This is useful for professional video primarily.</div><div><br></div><div><b>5) Backup as sparse as you are willing to recover from.</b></div>
<div><br></div><div>- If you couldn't stand losing more than a week's worth of data, you'd best be backing up weekly.</div><div>- If you couldn't stand losing more than a day's worth of data, you'd best be backing up daily.</div>
<div>- If you couldn't stand losing more than an hour's worth of data, you'd best be backing up hourly. </div><div><br></div><div>You know what is important and what is not. Make sure to taylor your backup routine to your needs. <span style="border-bottom:1px dashed rgb(0, 102, 204)">Incremental backups</span>, such as Time Machine are good about
this.</div><br><br><br>--- On <b>Sun, 11/29/09, John Robertson <i><<a href="mailto:john@createmydvd.com" target="_blank">john@createmydvd.com</a>></i></b> wrote:<br><blockquote style="border-left:2px solid rgb(16, 16, 255);margin-left:5px;padding-left:5px">
<br></blockquote>From: John Robertson <<a href="mailto:john@createmydvd.com" target="_blank">john@createmydvd.com</a>><br>Subject: [DM-MUG] Using RAID with Tiger<br>To: "Des Moines Mac Users Group" <<a href="mailto:dmmug@dmmug.org" target="_blank">dmmug@dmmug.org</a>><br>
Date: Sunday, November 29, 2009, 11:52 AM<div><div></div><div class="h5"><br><br><div>Just wondering if anyone has any experience using RAID on a single <br>user OS. I purchased a new 1TB drive and I was thinking of <br>
partitioning it to use as a mirror for my 500G drive. I have two <br>questions before I attempt this. The 1st question is, will it erase <br>the contents of the old drive (the 500 gig) that I am adding the 1TB <br>to when I turn on RAID? Also, what are the differences between RAID <br>
mirrored and RAID Striped? I understand how
Mirroring works and a <br>little about RAID 5 (which is only available on servers) but I don't <br>know which of the other option available here would be better to use.<br><br>Thanks,<br> John<br><br>_______________________________________________<br>
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