Considering that Software RAID is used on many a server (I have one XServe that doesn't have a RAID card that is running Software RAID for instance) it is fine for normal users. It does slow your computer more than a hardware-based machine, but not enough to recommend its non-use.<br clear="all">
-- <br>Jon Thompson<br>Evolve<br><a href="http://www.dmevolve.com">www.dmevolve.com</a><br>
<br><br><div class="gmail_quote">On Mon, Nov 30, 2009 at 2:40 AM, Matt Stanton <span dir="ltr"><<a href="mailto:inflatablesoulmate@brothersofchaos.com">inflatablesoulmate@brothersofchaos.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
Bleh, it was bound to happen, but I got the raid types confused halfway<br>
through the email.<br>
<div class="im"><br>
Where I said:<br>
<br>
RAID0 is only really useful if you need to be able to hotswap the failed<br>
drive. Otherwise, it makes much more sense to use two drives of the<br>
same size and do regular or incremental backups.<br>
RAID1 is dangerous, and only useful if you need to be able to read/write<br>
data to a hard drive much faster than a normal user.<br>
<br>
<br>
</div>It should read:<br>
<br>
RAID1 is only really useful if you need to be able to hotswap the failed<br>
<div class="im">drive. Otherwise, it makes much more sense to use two drives of the<br>
same size and do regular or incremental backups.<br>
</div>RAID0 is dangerous, and only useful if you need to be able to read/write<br>
<div class="im">data to a hard drive much faster than a normal user.<br>
<br>
<br>
<br>
</div><div><div></div><div class="h5">Matt Stanton wrote:<br>
> Here are some of the pros and cons of RAID setups:<br>
> RAID0 (striping): 2 500GB drives == One RAID volume of 1000GB<br>
> pros:<br>
> Twice the data transfer throughput of a single HD<br>
> Only requires 2 HDs<br>
> You have the amount of space of both hard drives combined<br>
> cons:<br>
> If one drive fails, you lose all the data on both drives<br>
><br>
> RAID1 (mirroring): 2 500GB drives == One RAID volume of 500GB<br>
> pros:<br>
> Only requires 2 HDs<br>
> If one drive fails, you still have all of your data<br>
> cons:<br>
> No speed boost over a single drive<br>
> You have only half the combined storage space of both hard drives.<br>
><br>
> RAID5 (striping + parity): 3 500GB drives == One Raid volume of 1000GB<br>
> pros:<br>
> Twice the data transfer throughput of a single HD<br>
> If one drive fails, you have half your data, plus enough parity data to<br>
> regenerate the other half<br>
> cons:<br>
> If one drive fails, you not only lose the throughput of the second drive<br>
> (you drop to the throughput of a single drive), but any data that was<br>
> lost on the failed drive must be regenerated from the two surviving<br>
> drives when you access the data (this shouldn't cause an additional<br>
> performance drop, since the hard drives are where the speed bottlenecks,<br>
> but if you are using software RAID, it would mean extra processing on<br>
> the CPU)<br>
> Requires at least 3 equally-sized hard drives<br>
><br>
> RAID10, RAID0+1, RAID1+0, RAID1&0 (striping + mirroring): 4 500GB drives<br>
> == One Raid volume of 1000GB<br>
> pros:<br>
> Twice the data transfer throughput of a single HD<br>
> Data can survive the failure of 2 HDs<br>
> If 1 or 2 drives fail, you retain the throughput performance of the<br>
> striped array<br>
> cons:<br>
> Requires 4 drives and gives you half the combined space of those 4 drives<br>
><br>
> There are also RAID3 and RAID4, which are similar to RAID5, in that they<br>
> are a mirrored+parity array (they just handle the parity differently<br>
> than the RAID5 array does). RAID6 is a mirror+parity type of array that<br>
> uses 2 parity drives so that it can survive the loss of 2 drives, where<br>
> RAID3,4,5 would only be able to survive the loss of 1 drive.<br>
><br>
> RAID0 is only really useful if you need to be able to hotswap the failed<br>
> drive. Otherwise, it makes much more sense to use two drives of the<br>
> same size and do regular or incremental backups.<br>
> RAID1 is dangerous, and only useful if you need to be able to read/write<br>
> data to a hard drive much faster than a normal user. It would be<br>
> recommended for use as the drive that the operating system and<br>
> applications are saved to (since you can usually reinstall the OS and<br>
> Applications from their original media). All data/documents should be<br>
> saved to a separate drive.<br>
> RAID5 is especially useful in a server environment, since it allows the<br>
> server to continue functioning even if a drive dies. Generally the<br>
> server supports hot-swappable drives so that when a drive fails, you<br>
> simply pull it out and replace it with a new drive, and the data is<br>
> automatically regenerated with the server still running. RAID5 is also<br>
> a better choice if you don't have the money for the more expensive<br>
> RAID10 style arrays.<br>
> RAID10 is the most fault-tolerant of the arrays, while also giving you<br>
> extra speed. This type of array is the most expensive, though, since<br>
> you get only half the storage space of the 4 drives.<br>
><br>
> The only RAID type that is of much noticeable benefit on a desktop<br>
> computer is RAID0. Many people use a RAID0 array as a temporary storage<br>
> area for programs that do large amounts of data manipulation, such as<br>
> video editing. In the windows world, it is often used on gaming<br>
> computers to reduce game load time. In either case, everything on the<br>
> RAID0 array should be backed up to a secondary location regularly.<br>
><br>
> All of the other raid types are used for either a mix of performance and<br>
> data safety or for data safety on its own. You would get the same level<br>
> of safety if you simply back up all of your important data regularly.<br>
> RAID mirroring will not protect your data against accidental deletion or<br>
> overwriting, which is why backups are important.<br>
><br>
> I am a bit leery of Software RAID (which is what is present on most<br>
> desktop computers these days). Since the array is dependent on the OS<br>
> to achieve the results, you are still using processor power and sending<br>
> extra data over the SATA/IDE bus. Hardware RAID was/is available in<br>
> many Macs (at least, I have seen it available in the Mac Pro line), and<br>
> if you have the hardware RAID card, then you would be well-served to use<br>
> it (assuming you can afford the extra hard drives).<br>
><br>
> - Matt<br>
><br>
> Jon Thompson wrote:<br>
><br>
>> Please note that the article Anastasia reposted to the list is<br>
>> available on my company website <a href="http://www.dmevolve.com" target="_blank">www.dmevolve.com</a><br>
>> <<a href="http://www.dmevolve.com" target="_blank">http://www.dmevolve.com</a>>, as well as other articles.<br>
>><br>
>> Anastasia has it wrong. If we're talking about support beams...<br>
>><br>
>> - RAID1 is making sure that every beam is at 50% capacity- you can<br>
>> lose half and your building won't fail.<br>
>> - RAID0 is making sure that every beam is at 100% capacity- you can't<br>
>> lose a single beam without losing the building.<br>
>><br>
>> RAID0 takes individual files, divides them in half and splits them<br>
>> between drives, so if you lose one drive, you've lost all of your<br>
>> data. This doubles the write speed of the drives, which is why it is<br>
>> used at all, for specific purposes, which are _always_ stored<br>
>> elsewhere as well.<br>
>><br>
>> Striped is RAID 0 and like I said, increases the likelihood of data<br>
>> loss. Avoid it unless you know exactly why you want it. RAID 1<br>
>> performs the exact function of making a SuperDuper or Carbon Copy<br>
>> Cloner mirror of your drive. Except that it does it better, as it is<br>
>> in real time. It _only_ protects you from disk failure, which is<br>
>> actually a rarity, unless your drive is very new or very old. In the<br>
>> latter case, it is a better idea to get a new drive, burn it in for<br>
>> two weeks, then migrate your data to it using CCC.<br>
>><br>
>> As for configuring a RAID. Disk Utility will wipe all drives when<br>
>> creating a RAID. However, it is possible to do it without wiping the<br>
>> drive using the diskutil command line application. Please do not do<br>
>> this unless you are comfortable with the commands and how to modify<br>
>> my examples to suit your needs. I am not teaching you how to get to<br>
>> the command line. If you don't already know, this is not the set of<br>
>> commands for you, as there is a very real chance to lose your data.<br>
>><br>
>> diskutil list (pay attention to the drivenumbers, which are listed as<br>
>> "disk#". Most Macs have a boot drive of disk0)<br>
>> diskutil enableRAID mirror disk<drivenumber of main boot partition><br>
>> diskutil repairMirror disk<drivenumber of main boot partition><br>
>> disk<drivenumber of empty drive><br>
>><br>
>> The other thing is that the 1 TB drive will effectively become 500 GB,<br>
>> wasting the remaining space. I do not believe it is possible to<br>
>> partition part of a drive that is used in RAID, but could be wrong, as<br>
>> I _never_ use non-matching drives in RAID, like you are wanting to do<br>
>> here. Part of this is I/O. It is imperative that data is written to<br>
>> the two hard drives simultaneously, otherwise, data corrupting<br>
>> bottlenecks are possible. Since one hard drive is now responsible for<br>
>> two partitions, it no longer has 100% of it's time dedicated to<br>
>> maintaining the RAID.<br>
>><br>
>> Finally, the only way that I would consider doing a software based<br>
>> raid is if you have two internal drives, such as in a MacPro, XServe,<br>
>> or the new Mac Mini Server. DO NOT DO RAID OVER FIREWIRE. (Unless you<br>
>> are buying a RAID-based device like a Drobo, or the better performing<br>
>> Promise SmartStor DS4600, which house all drives internally.) If you<br>
>> have one drive internal, and the other over firewire and you pull the<br>
>> cord out, you are going to rebuild your RAID. Same with the power<br>
>> cord. It's just not a good idea, as you are increasing the likelihood<br>
>> of compromising your redundancy.<br>
>> --<br>
>> Jon Thompson<br>
>> Evolve<br>
>> <a href="http://www.dmevolve.com" target="_blank">www.dmevolve.com</a> <<a href="http://www.dmevolve.com" target="_blank">http://www.dmevolve.com</a>><br>
>><br>
>><br>
>> On Sun, Nov 29, 2009 at 7:05 PM, AB <<a href="mailto:anastasia_prittee@yahoo.com">anastasia_prittee@yahoo.com</a><br>
>> <mailto:<a href="mailto:anastasia_prittee@yahoo.com">anastasia_prittee@yahoo.com</a>>> wrote:<br>
>><br>
>> As I understand it...<br>
>> RAID Mirrored mirrors the contents and files of a single drive in<br>
>> the event that drive fails—see excerpts from the info Jon gave.<br>
>> RAID Stripped takes content and distributes it across multiple<br>
>> drives. Kind of like putting multiple support beams in. Each hard<br>
>> drive is a support beam and collectively behave as one unit. One<br>
>> of those drives failing won't necessarily have detrimental<br>
>> repercussions. I believe John Thompson gave a detailed<br>
>> description. Though I might be confused on this.<br>
>><br>
>> As far as erasing contents on the existing drive, I'm not sure and<br>
>> was wondering the same thing myself.<br>
>><br>
>> Here's what I saved for reference on what was mentioned before<br>
>> about RAID. I thought there was another detailed summary, Jon<br>
>> gave, but I this seems to be all I saved.<br>
>><br>
>> Jon Thompson wrote this on May 19, 2009:<br>
>><br>
>> *1) A good backup is a verifiable backup*<br>
>><br>
>> If you are dumping info into Time Machine, and you are _never_<br>
>> pulling info back out of it and checking, how do you know that the<br>
>> data is good? In the instance of the SideKick data, this means<br>
>> that they would have known that the backup is good, and that they<br>
>> could rely on it. Until you know that you can recover from it, you<br>
>> cannot call it a good backup.<br>
>><br>
>> *2) A good backup consists of many backups of the same data.*<br>
>><br>
>> I store three months of backups, and I consider that too little,<br>
>> but don't dare increase my budget. If you are relying on all of<br>
>> your data being on a single hard drive, what happens if there is a<br>
>> fire and both your computer and backup is lost? If all of your<br>
>> backup is in one cloud (Mozy) and that cloud bursts like the<br>
>> SideKick cloud did, you are hosed. Now, if you have daily backups<br>
>> on a time machine volume, and a weekly backup to Mozy, you are<br>
>> protected from either example. Mozy is your offsite backup, the<br>
>> time machine<br>
>><br>
>> *3) Synchronization is not backup.*<br>
>><br>
>> Synchronization ensures that all of you data is the same between<br>
>> all instances that you create. If you are syncing your address<br>
>> book on your mac with an iPhone, you have two instances of the<br>
>> data, but they are tied together. If you delete a contact on one<br>
>> (or a virus deletes all of them) that deletion is transferred to<br>
>> your backup. I realize that there are ways that the sync service<br>
>> tries to reduce the chance of this, but it is still a possibility.<br>
>> However, an offline copy of your address book on a USB thumb drive<br>
>> that is not plugged into your computer cannot not be changed, at<br>
>> least until it is plugged in again. Dropbox is a synchronization<br>
>> service.<br>
>><br>
>> *4) RAID is not backup.*<br>
>><br>
>> RAID (except 0) is a way to protect from hard drive crashes. It<br>
>> does not protect from application corruption, accidental deletion,<br>
>> or intentional deletion. All of which are much more likely than<br>
>> hard drive corruption during the majority of the life of a hard<br>
>> drive. RAID is useful for server admins that deal with<br>
>> distributing data amongst many hard drives, which actually is a<br>
>> great way to exponentially increase the likelihood of data loss<br>
>> due to hard drive failure.<br>
>><br>
>> RAID 0 offers no protection at all- in fact, it is will<br>
>> exponentially increase your likelihood of data loss due to hard<br>
>> drive failure. Be careful when purchasing large external hard<br>
>> drive, as they are sometimes two drives that are internally<br>
>> configured as RAID 0. This is useful for professional video primarily.<br>
>><br>
>> *5) Backup as sparse as you are willing to recover from.*<br>
>><br>
>> - If you couldn't stand losing more than a week's worth of data,<br>
>> you'd best be backing up weekly.<br>
>> - If you couldn't stand losing more than a day's worth of data,<br>
>> you'd best be backing up daily.<br>
>> - If you couldn't stand losing more than an hour's worth of data,<br>
>> you'd best be backing up hourly.<br>
>><br>
>> You know what is important and what is not. Make sure to taylor<br>
>> your backup routine to your needs. Incremental backups, such as<br>
>> Time Machine are good about this.<br>
>><br>
>><br>
>><br>
>> --- On *Sun, 11/29/09, John Robertson /<<a href="mailto:john@createmydvd.com">john@createmydvd.com</a><br>
>> <mailto:<a href="mailto:john@createmydvd.com">john@createmydvd.com</a>>>/* wrote:<br>
>><br>
>><br>
>> From: John Robertson <<a href="mailto:john@createmydvd.com">john@createmydvd.com</a><br>
>> <mailto:<a href="mailto:john@createmydvd.com">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">dmmug@dmmug.org</a><br>
>> <mailto:<a href="mailto:dmmug@dmmug.org">dmmug@dmmug.org</a>>><br>
>> Date: Sunday, November 29, 2009, 11:52 AM<br>
>><br>
>><br>
>> 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>
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</div></div></blockquote></div><br>