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abishur
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Re: File and/or media server

Wed Aug 31, 2011 6:49 pm

Okay guys, I'm seeing the disconnect here. I'm talking about backup in the average home user sense. You know people who can't afford an offsite location nor want to spend double the cash every time they want to increase their storage space. If it makes you feel better, I'll stop calling it a "backup" and refer to it as "increased redundancy"

For the average home user RAID 5 is the perfect data redundancy solution. It provides hard drive failure protection which is the most common cause for data loss. Yes that won't protect against multiple drives dying at once, but that's happened once (they weren't in raid or anything just in the same computer) to me in 15 years of IT work and that was because they were crappy drives.

Of course it won't protect against natural disasters, but what if a comet strikes the earth and your data is lost because you weren't smart enough to have off planet data storage? :P

Forgiving the sarcasm, my point is that there comes a point of worthwhile "backup" solutions. For businesses, I'm am 100% in agreement with you. For the average home user (by which I mean mean me)? Maybe some of them can afford something like Carbonite or Mozy or some other form of cloud backup solution. I know that I can't. And for these people RAID 5 is the best option available. It provides redundancy, it protects against hard drive failure, it allows the addition of more drives so it's scalable. It's a great solution for people who don't have the dough to pay for "true" backups.
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obarthelemy
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Re: File and/or media server

Wed Aug 31, 2011 7:09 pm

@abishur: with the price of HDs so low, I went for a single 3TB one, and recycled an older 2TB one as a backup, leaving .. some stuff... out of the backups. 2TB is 64€ list, with frequent sales; add 20€ for an enclosure. The time I spent ripping my 1,000+ CD collection to FLAC is worth that, and more.

Svartalf
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Re: File and/or media server

Wed Aug 31, 2011 7:09 pm

No, actually, it's not, abishur. Lose a disk, you are at risk. Lose two (which is likely...seen it...seen it often actually... Your experience isn't the norm, actually- and I can hand you a handful of links discussing the concept that what everyone "knows" about disks is wrong, including about RAID... ;) ) and you've lost everything. RAID was never intended for backup- only to expand overall capacity with cheaper disks and to keep a system up in the case of a disk failure so it didn't crash outright.

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abishur
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Re: File and/or media server

Wed Aug 31, 2011 8:00 pm

@obarthelemy I could afford one drive at that price, but not two (which is another great thing about RAID 5, dynamically expandable. I buy what I need when I need it).

@Svartalf I already dropped the word "backup" since that was unacceptable. I'm just calling it what it is, "increased redundancy". You're arguing a point I've already conceded. What I am arguing is that for the standard home user RAID 5 is the perfect blend of cost to disk space ratio for protecting data from the most common form of data loss, total disk failure.
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Lob0426
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Re: File and/or media server

Wed Aug 31, 2011 8:53 pm

The fact is I took all of this into consideration when I built my own home "backup". For my solution I chose WHS (Windows Home Server). But I also took other steps first of all, I bought each of the two drives from different manufacturers. This way you do not have a hardware fault that is likely to fail at the same time. I back up the operating system itself at regular intervals. A better solution would be to have two totally different hardware devices. Two different distros, one on each device. Each device running RAID 1, yes RAID 1. And each having a different brand of HDD.

What I am seeing here is a solution that is too complicated for the average home user. As abishur pointed out, you can not have a 100% solution. You protect against the most likely, audit your assumptions periodically and make changes after you find reason in that process.

I am ready for the beating so bring it.

My suggestion for the "average" home user. A RasPi, two 1TB (minimum) drives different brands, a stable distro of Linux. Software RAID1, Setup a batch file to backup up the client computer in a timely manner. KISS. You do not need to worry about up time. This is not a business solution. I turn my WHS off when I don't need it. You want it out of the house? Put it in a shed or a even a bird house as long as you can get power and Ethernet to it. Encryption would be nice.
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obarthelemy
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Re: File and/or media server

Wed Aug 31, 2011 9:05 pm

Abishur, you're sure that multi-drive enclosure and RAID card won't cost significantly more than a couple of 2 TB HDs ? The cheapest 3+ drive external enclosure my usual retailer carries is the Icy Box IB-RD3262 @ 170 euros, which is more than 2x2TB disks +2 dumb enclosures. Plus you can offset some of the cost by selling on your old drives. I'm guessing you can't do software raid5 over a single USB channel.. or don't want to, even if it's possible ^^
Pro-tip for RAID and backups: don't buy drives from the same series, or even the same manufacturer, so that a faulty batch doesn't fail you all at the same time. Some raid controllers do require identical drives, which is kind of a paradox...

swaite
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Re: File and/or media server

Wed Aug 31, 2011 9:15 pm

For an easy, actual backup, have your live data stored on whatever (desktops, NAS, etc), and a separate box running the backups. Offsite might be much for a lot of home users, but if they actually value their data, they'll have it in at least 2 places - live on their machines, and then on an external hard drive that is -ONLY- used for backups. No live access of data from it. This is where the R Pi shines, you can snag a cheap enclosure, drop a drive in, and then add the $35 for an R Pi B. Yes, it's not the best backup situation, your data is being entrusted to a single drive.

I know a lot of people that buy a matched pair of external USB hard drives - backup to one, take it into the office, then do regular backups on the other. Every week or three, switch the drives. That way, you have a contingency plan. My coworker bought a pair of 3TB WD externals with USB3 for $150/each.

One of the difficulties with the different brand thing is that there are so few left...Seagate, WD, and one other (Hitachi, maybe?). Everyone is rebranding their drives, or slapping the drives in a different enclosure. It's not a bad idea to do so, whenever possible.

RAID1 is perfectly okay for a home user, as well, though RAID5 or RAID6 would be better.

Anyway, these things will make a pretty good NAS for backups, live storage, or whatever. Cheap, can run linux, and has the onboard ports that are required.

obarthelemy
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Re: File and/or media server

Wed Aug 31, 2011 9:16 pm

@lob: agreed, especially about mixing hard disks.

Also, it's probably worth differentiating user-generated content (docs, photos, mails...) and other media (rips, downloads, torrents...). The first are irreplaceable, I burn a DVD with it whenever I go visit my parents, drop it off in their safe, and keep old copies. The second is kind a pain to lose, but can be replaced if needs must, so I just put it on another HD which I put in a drawer at work.

I guess that's a professional hazard. I've seen too many people lose everything, I got paranoid, and I've seen so many RAID horror stories I'm convinced the thing actually increases the risk of data loss, but that also maybe because RAID-ed data has high visibility. A hard disk dying is low-key bad luck, a raid array dying is a high-visibility outrage ^^ I've really been bitten, in my professional career, by RAID arrays I had sold.

OK, I'll shut up on the subject now.

DanielSilva
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Re: File and/or media server

Wed Aug 31, 2011 9:18 pm

RAID-Z. Enough said ;)

Svartalf
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Re: File and/or media server

Wed Aug 31, 2011 9:31 pm

Quote from abishur on August 31, 2011, 21:00
@Svartalf I already dropped the word "backup" since that was unacceptable. I'm just calling it what it is, "increased redundancy". You're arguing a point I've already conceded. What I am arguing is that for the standard home user RAID 5 is the perfect blend of cost to disk space ratio for protecting data from the most common form of data loss, total disk failure.

Heh... Most users think this stuff's magic- and they'd not realize that if they had a disk failure that it would be an imperative to get that disk replaced. They're as likely as not to ignore it until the next failure and lose everything anyway. And they can't just use any disk, willy-nilly, to replace it- it has to be the same model if at all possible and if not, it must be exactly the same size or larger. If you replace with a larger disk, you must replace the next failed disk with the same story, and so forth. You do realise that within the 500Mb size class there's at least 4 or 5 differing actual sizes within that space, all claimed to be 500Mb. Can you grab a box and tell me that one disk is the same size or larger? What about the 1Tb disks? What about 3Tb disks?

If you can't map a consistent safe path without a bunch of research and discipline through that minefield, then this isn't an answer to that problem you refer to.

I'm working on something, though, that might make the cut. :D

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Lob0426
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Re: File and/or media server

Wed Aug 31, 2011 9:33 pm

I am not a big fan of RAID either, I would prefer a non RAID solution such as software mirroring. This is completely possible in a dedicated device. WHS(first version not vail) does not work on RAID. Vail does rely on RAID so I will not switch to it. I have been very lucky and have never had a data loss that was total. The last time was on an IDE drive which would not work as a master but worked enough as a slave to retrieve the data. Not sure SATA is going to work that way. We need to think along the lines of software mirroring in Linux.
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Svartalf
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Re: File and/or media server

Wed Aug 31, 2011 9:33 pm

Quote from obarthelemy on August 31, 2011, 22:05
Some raid controllers do require identical drives, which is kind of a paradox...

Actually, it's not. You're really supposed to have a set of disks that're the same size (or larger...you can cheat there...). The only way to ensure that particular criterion is insisting on the same model on all drives in the array, including hot-spares.

Svartalf
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Re: File and/or media server

Wed Aug 31, 2011 9:35 pm

Quote from Lob0426 on August 31, 2011, 22:33
We need to think along the lines of software mirroring in Linux.

Heh... It's not ready for primetime on what we're looking for, but...

http://www.gluster.org

Svartalf
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Re: File and/or media server

Wed Aug 31, 2011 9:40 pm

Quote from swaite on August 31, 2011, 22:15
RAID1 is perfectly okay for a home user, as well, though RAID5 or RAID6 would be better.


Heh... Write the same data to two identical drives. Can you reliably tell me which data is correct or not?

You can't. Not unless you poll both drives after the write to ensure you've put the data right to the disks. Pretty much none of the RAID1 controllers will do this because that's a serious performance hit. RAID1 isn't a good idea, and really hasn't been from day 1 on the concept.

RAID5's probably useful, but it's technical requirements are a minefield that will lead to inconsistent results for the average user.

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Lob0426
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Re: File and/or media server

Wed Aug 31, 2011 9:40 pm

You can RAID different size drives. They will just default to the smaller drive size. You will not be able to use the left over space either. Somebody needs to build a drive extender version for Linux. It does not care what size each drive is it just adds all of it.
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Svartalf
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Re: File and/or media server

Wed Aug 31, 2011 9:55 pm

Quote from Lob0426 on August 31, 2011, 22:40
You can RAID different size drives. They will just default to the smaller drive size. You will not be able to use the left over space either.

Yes. However...if you plug a smaller disk into the array that you've already established...it's not going to work so hot, if at all, now is it?

I've seen many a disaster where the disk sizes were only a couple of blocks smaller (Vendor had disks with the same model # but the disks were differing geometries (WTF?)) hosing up a half million dollar value traffic monitor system, requiring a re-image job of the system by shipping a known good pair of RAID1 disks to the site and then re-installing from the baseline.

obarthelemy
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Re: File and/or media server

Wed Aug 31, 2011 10:00 pm

I seem to remember smarter raid controllers managing to use up all the space on all the disks whatever their sizes, but can't seem to find the info. Seems intuitively feasible though, with 3+ disks, if the largest drive is no bigger than all the other ones added.

@svartalf: the paradox is that RAID users usually expect reliability, but most RAID solutions push them to get all identical disks, presumably all at the same/purchase time ie from the same batch, which pretty much guarantees multiple simultaneous failures in case of a faulty production run. Disaster ensues to great dismay and much wailing ^^

Svartalf
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Re: File and/or media server

Wed Aug 31, 2011 10:02 pm

Quote from DanielSilva on August 31, 2011, 22:18
RAID-Z. Enough said ;)

Heh... Combine RAID-Z and gluster bricks and you might just have a win there. ;)

Svartalf
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Re: File and/or media server

Wed Aug 31, 2011 10:09 pm

Quote from obarthelemy on August 31, 2011, 23:00
I seem to remember smarter raid controllers managing to use up all the space on all the disks whatever their sizes, but can't seem to find the info. Seems intuitively feasible though, with 3+ disks, if the largest drive is no bigger than all the other ones added.


Heh... That would be a disaster. With one smaller disk, the larger disks wouldn't have the rotating parity chunk stored for them. It's a disaster looking for a place to happen. :D


@svartalf: the paradox is that RAID users usually expect reliability, but most RAID solutions push them to get all identical disks, presumably all at the same/purchase time ie from the same batch, which pretty much guarantees multiple simultaneous failures in case of a faulty production run. Disaster ensues to great dismay and much wailing ^^

Heh... There's another paradox... Google found that with three disks, your odds of a two-up failure on a RAID5 jumps significantly when you have the first failure. No production run failure needed. ;)

Unless your RAID controller uses turbocode FEC so that you don't need to worry about too many hard write failures to the disks, RAID1's not a good idea. It's still not too keen, based on what I've been privy to.

RAID5's only good for saving your butt from a single disk failure where you get someone to hot-plug a disk into the array as quickly as is possible.

DanielSilva
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Re: File and/or media server

Wed Aug 31, 2011 10:10 pm

We need to think along the lines of software mirroring in Linux.

Again i say this, RAID-Z. If you never tried using ZFS you really should. I converted my home fileserver from a purely hardware raid system ( 1+0 ) to a zfs based setup and i wish i would have done it earlier. The snapshot feature alone won me over.

The first thing i'll do when i get a raspi is connect a couple of hdds to it, throw zfs on it and make it a replication target to the main server.

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abishur
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Re: File and/or media server

Wed Aug 31, 2011 10:58 pm

Quote from Svartalf on August 31, 2011, 22:31

Heh... Most users think this stuff's magic- and they'd not realize that if they had a disk failure that it would be an imperative to get that disk replaced. They're as likely as not to ignore it until the next failure and lose everything anyway. And they can't just use any disk, willy-nilly, to replace it- it has to be the same model if at all possible and if not, it must be exactly the same size or larger. If you replace with a larger disk, you must replace the next failed disk with the same story, and so forth. You do realise that within the 500Mb size class there's at least 4 or 5 differing actual sizes within that space, all claimed to be 500Mb. Can you grab a box and tell me that one disk is the same size or larger? What about the 1Tb disks? What about 3Tb disks?

If you can't map a consistent safe path without a bunch of research and discipline through that minefield, then this isn't an answer to that problem you refer to.

I'm working on something, though, that might make the cut. :D

It's true setting up a RAID array takes a bit of intelligence (like replacing a drive when it goes bad, I have to admit I've run into people who who didn't replace the bad drive and then were indeed shocked when a second disk went bad some time later and all data was lost :P ). You slap a couple drives together and then get surprised when it actually reduces the life of the drive (which is what RAID 0 does by the way), but if you research the drive a little before buying it (maybe even look at the tech document from the manufacture) you can find out what they define a byte as and make sure to get the right sized drive.

Worst case scenario though, when a disk goes bad in RAID 5 (or dare I even say RAID 6) I replace it with a larger disk. By the time a disk goes bad it's usually time for a space upgrade anyways. Yes the additional space will be lost at first, but once all the disks are replaced, the size will increase. It's a very nice way to progressively increase your RAID size.

@obarthelemy - Yeah, I came to the same conclusion. I only have 1 drive right now, so the whole thing is slightly moot :P
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abishur
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Re: File and/or media server

Wed Aug 31, 2011 11:30 pm

Oh, and I'm also interested checking out the RAID-Z suggestion :)
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patrickhwood
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Re: File and/or media server

Wed Aug 31, 2011 11:32 pm

We run a commercial RAID5 system at our office for network storage (Samba & NFS). There's a hot spare in the box, and if a disk dies, it emails the admin to make sure we replace it so we still have a hot spare. It'll prompt on a new drive that's too small as a hot spare, either letting us put a larger one in or resizing the file system in the background (if there's free space available) so the hot spare *is* usable (the wonders of LVM).

patrickhwood
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Re: File and/or media server

Wed Aug 31, 2011 11:33 pm

And back to the original idea -- what about a local NAS to cloud server? Something that talks to box.net storage or amazon S3 and shares that locally over samba?

Blars
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Re: File and/or media server

Thu Sep 01, 2011 1:09 am

A good software raid system will let you do tricks like mirroring two 2gig drives to a 4gig drive, migrate partitions between disks on a running system, etc. Just add a new bigger disk, migrate some partitions around, and grow the filesystems. I never found a hardware raid system anywhere near as versital as raid on top of LVM. (as opposed to LVM on top of raid, which some people seem to prefer.)

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