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ed71

RAID for music storage

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After deciding that I probably do not need a NAS for my music library, I am planning to get a new external hard drive or two. That brings up the RAID or non-RAID question, so I want to make sure I am understanding this correctly. It seems like the only advantage of RAID (RAID 1, Drobo, etc.) for an external drive that will be used only to store my iTunes library would be storage capacity. Is that correct, or are there other benefits I'm forgetting?

 

Since my music storage needs are nowhere close to 4TB (probably more like 1TB), it seems like I'd be better off skipping RAID for that drive. Assuming that RAID drives work well with Time Machine, I might consider one as a full system backup option at some point, but I probably don't need that much space now.

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The basic principle of RAID is that it keeps (at least) two copies of everything; the different types of RAID do this in different ways to give different levels of security and performance. The benefit of course is that you are less likely to lose data since if one disk fails the other is available while the dud one is swapped out. The downside is that you halve the available space and may get slower performance. To use RAID you need two disks (in theory it could be two platters in a single drive but that is a bit useless when things go wrong). Typically a NAS would have space for example for two 2TB drives and when set up for RAID you would end with 2TB of storage space for the cost of 4TB.

 

When considered as a form of backup, RAID has the disadvantage of being all in one place so many forms of disaster would affect both original and backup. Personally, I prefer to backup to a disk on a different machine, or at the very least a different external drive and in the cloud as well. RAID is really meant for volatile, heavily-used business systems.

 

Mike

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After deciding that I probably do not need a NAS for my music library, I am planning to get a new external hard drive or two. That brings up the RAID or non-RAID question, so I want to make sure I am understanding this correctly. It seems like the only advantage of RAID (RAID 1, Drobo, etc.) for an external drive that will be used only to store my iTunes library would be storage capacity. Is that correct, or are there other benefits I'm forgetting?

 

Since my music storage needs are nowhere close to 4TB (probably more like 1TB), it seems like I'd be better off skipping RAID for that drive. Assuming that RAID drives work well with Time Machine, I might consider one as a full system backup option at some point, but I probably don't need that much space now.

 

What a RAID does depends on the type of the RAID - aka the RAID level. Only level 0 has no redundancy. All other levels are about redundancy, not capacity. Speed (reading, writing) is another important consideration.

 

RAID Level 0 (Striping):

* N harddisks of C gigabytes capacity

* total capacity is N x C

* ca. N times read speed

* ca. N times write speed

* no redundancy, i.e., one drive fails, the whole RAID is lost

Summary: not recommendable except for temporary data, better use e.g. LVM

 

RAID Level 1 (Mirroring):

* N harddisks of C gigabytes capacity

* total capacity is C

* ca. N times read speed

* write speed same as single harddisk

* RAID only loses data if all N disks fail

Summary: great for higher read speed and data safe-keeping - backup still necessary!

 

RAID 4:

* N harddisks of C gigabytes capacity

* total capacity is (N-1) x C

* (N-1) times read speed

* typically same as single hard disk write speed

* redundancy allows exactly 1 disk to fail, data loss after that

Summary: good capacity, but not ver efficient on writes - minimal redundancy

 

RAID 5:

* N harddisks of C gigabytes capacity

* total capacity is (N-1) x C

* (N-1) times read speed

* (N-1) times write speed

* redundancy allows exactly 1 disk to fail, data loss after that

Summary: more efficient version of 4

 

RAID 6:

* N harddisks of C gigabytes capacity

* total capacity is (N-2) x C

* (N-2) times read speed

* (N-2) times write speed

* redundancy allows up to 2 disks to fail, data loss after that

Summary: like 5, but more redundancy for less speed and capacity

 

RAID 10 (stripe of mirrors)

* N x M harddisks of C gigabytes capacity (typicall N=M=2, i.e. 4 disks)

* total capacity M x C

* up to NxM read speed

* M times write speed

* redundancy allows up to (N-1) x M disks to fail provided that of each N mirrored harddisks one survives

Summary: good compromise of speed and redundancy, popular with 4 disks

 

Personally, I would go RAID 10 or RAID 1, but for home use I cannot see RAID 6 being very attractive (pays off when using ca. 8 disks or more).

 

Cheers,

Peter

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Jud   
What a RAID does depends on the type of the RAID - aka the RAID level. Only level 0 has no redundancy. All other levels are about redundancy, not capacity. Speed (reading, writing) is another important consideration.

 

* * *

RAID Level 1 (Mirroring):

* N harddisks of C gigabytes capacity

* total capacity is C

* ca. N times read speed

* write speed same as single harddisk

* RAID only loses data if all N disks fail

Summary: great for higher read speed and data safe-keeping - backup still necessary!

 

* * *

Personally, I would go RAID 10 or RAID 1, but for home use I cannot see RAID 6 being very attractive (pays off when using ca. 8 disks or more).

 

Cheers,

Peter

 

Hang on, isn't effective capacity of a mirrored pair a single disk?

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Hang on, isn't effective capacity of a mirrored pair a single disk?

 

Exactly. If you have N disks of C gigabytes *each*, then the total capacity of a mirrored pair (N = 2) or any other mirrored number disks is C gigabytes, i.e., the capacity of one disk.

 

Sorry for being ambigious here.

 

Cheers,

Peter

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External harddrives are convenient because they can be used as backup media, although they are not very reliable backup media (but then again, neither are recordable optical discs).

If you are considering RAID for music storage, you might as well consider the fact a RAID array can protect important data against the risk of a harddrive failure only. Meaning, all data stored on the RAID array can still be lost in the event of a hacker / trojan / virus attack, a user / software error, or a hardware failure such as a SATA controller / Power Supply Unit failure. Therefore, they should NOT be seen as a backup strategy.

The reason why RAID 1 can still be useful is because the system can still continue to function normally if a harddrive fails (for example, in the financial world / accounting business, where each data transaction requires an instant backup, mirroring can be used as an additional safety measure to warrant system uptime reliability). With RAID 1 if duplexing is used, the data can be protected against the added risk of a hardware controller failure. To save on cost, cheaper alternatives, such as RAID 5 or RAID 6, may be considered (at the expense of uptime reliability and performance related factors).

Another downside of RAID is that, even if no data was lost, it can take a long time to rebuild a corrupted RAID array. If the RAID controller hardware fails, one should also mind the fact a compatible replacement needs to be readily available to be able to access the data (various horror stories can be found about scenarios where no compatible replacement could still be obtained at a reasonable cost, or where it took ages for a replacement to be delivered, or both).

Decent RAID controller hardware is expensive, but for home use I think a quality computer motherboard based around a modern Intel chipset, which typically always comes with an onboard RAID controller nowadays, can still be a valid choice after all (although depending on what exactly it is that people are planning to use it for........). Similarly, software RAID (which is a feature of Windows 7 Professional and higher editions, for example), or even the combination of both hardware (or onboard) and software RAID can still be a valid choice also, especially in terms of cost versus performance. These days, thanks to relatively new technologies such as ASUS SSD Caching, for example, the possibilities seem near endless, as with DDR3 RAM sticks becoming ever cheaper still, it now even looks like throwing, for another example, Romex Software Primo Ramdisk into the mix couldn't hurt much anymore, either.

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I know it's been written in other places here in C.A. and other boards, but I think that if you've just got simple home user's typical music library (ok perhaps I should be more specific) then keeping the data protection as simple as possible is the best way. I've gone through this thought process so much over the past few months in rebuilding my system. But straight backup was the solution I chose, for simplicity.

 

I love the concept of RAID1 or higher and I've implemented it in various ways before. The idea of having the data instantly there just sounds so neat to me (geek appeal?). But in the end my considerations were (and I don't pretend to assume that my requirements are like anyone else's):

 

- What was my biggest risk (= probability of it happening * impact of it happening)

 

Um, a drive failing and losing any of my music, movies etc (just under 1 TB). Impact: Long-term depression at losing the music I've been gathering for over 20 years (this goes back to tracker files in pre-MP3 days :-) )

 

- What was my main requirement if it did happen

 

Um, get the music back within 24 hours or so with little hassle or $ spend

 

- Do I need high data R/W performance from the media server

 

No. I add about an album a week, and don't care how long backup takes, as long as it doesn't mess with the sound quality. And there's plenty written about various RAID levels, implementations and the performance gain or hit they bring in.

 

With these requirements in mind, I just went for a regular external drive backup off the music server (Vortexbox just now, but have used NASs). Simple enough to recover files, and I'd only lose whatever didn't make the backup that day if I'd added it. Ok so to be sure, I set up another backup across the LAN to a NAS drive I had sitting elsewhere. That's enough cover for me. Rsync etc for the backup etc are all options to consider - depending on OS and your level of confidence in setting them up and more importantly bringing data back (see below). As my server is virtual, I just copy the virtual disk file using a Windows arrangement, once a day. Rsync is probably way more efficient and faster but messing with a USB 3 drive via free virtual hosting software was a challenge for me and the software.

 

Some older RAID arrangements do require similar disks to be used as replacements. I know that when my Japanese I-O Data RAID5 NAS eventually loses a drive (it's over 5 years old) I'll be looking for a 256gb IDE drive to replace. Fat chance - I'll have to downscale the thing to a RAID0 box or throw it away. So it's just operating as a secondary backup target today, as mentioned.

 

One thing I always do when changing arrangements around backup - TEST that I can actually RECOVER my data back to the way it was (tags, covers and associated stuff all intact). Whatever option(s) you go with, don't assume that like magic everything will be instantly accessible and recoverable. Do a real restore or drive hotswap&rebuild test if you can and don't just wait for it to happen. Especially when it comes to anything where you're less confident (like messing with lost Linux volumes through virtualisation etc for me). Some funny little extra things that needed to be done, I simply wrote down as I learned them, and stuck that bit of paper in a drawer for when the bad day comes.

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