drobo alternative

[pjkenned]

RAID 6 is also a cool tech but it is more like RAID 5 with dual parity (not all that much unlike Netapp's RAID 4 approach.)

NetApp's Raid 6 is more like Raid-DP.

Also, I'd rather have two raid 6 arrays than one raid 60 array anyday. Aside from the obvious higher chance of failure for a given set of drives with raid 60 over two raid 6 arrays (because one array becomes dependent on the other in raid 60) things like migrating Raid 60 arrays doesn't work on Adaptec controllers, whereas you can physically move an two entire raid 6 arrays from a say 3085 to 5805.

And that GPT on WHS... I will certainly be trying that! AWESOME LINK!!!!! I don't mind maintaining 2TB partitions if I can make more than 4 (in fact I'd rather make more smaller partitions than fewer big ones for WHS)

 

[imagoon]

NetApp's Raid 6 is more like Raid-DP.

Also, I'd rather have two raid 6 arrays than one raid 60 array anyday. Aside from the obvious higher chance of failure for a given set of drives with raid 60 over two raid 6 arrays (because one array becomes dependent on the other in raid 60) things like migrating Raid 60 arrays doesn't work on Adaptec controllers, whereas you can physically move an two entire raid 6 arrays from a say 3085 to 5805.

Statistically, You will lose 50% of your data with 2 x RAID 6 before a RAID 61 fails. Of course you have 1/2 the space. Once you go over a certain capacity you need worry about enclosure loss and the chance of multidisk failure. 99.9999% sounds great until you realize that huge arrays like this can have millions of sectors which even at 99.9999% = 1 sector per million will be bad, which is what RAID 60 is designed to handle (with the correct controller and arrays.) Basically here the "1 in a million chance" = dead multi-failed array.

There is a point, where the space to $ ratio means less than the data security value. For example, if you do a 2TB 15 Disk RAID 5 for 28TB of space, in all honestly you should be fired. Even RAID 6 or RAID 4 / DP is asking for high odds that should a single fail out that there will be far to many sectors to churn through to risk that the array will fine another bad sector, freak and drop the array.

EDIT: I just realized I have the RAID type wrong. I meant "RAID 61" IE Mirrored RAID 6 sets. Also I am aware that "61" is rare / not directly existent except via SAN replication and in most cases at that point most go with mirrored RAID 5 or "51"

 

[pjkenned]

EDIT: I just realized I have the RAID type wrong. I meant "RAID 61" IE Mirrored RAID 6 sets. Also I am aware that "61" is rare / not directly existent except via SAN replication and in most cases at that point most go with mirrored RAID 5 or "51"

I only brought up the raid 60 lowering reliability thing because if someone had searched for this, they may be given the wrong idea.

On the enclosure loss... I'm quite scared of that actually.

 

[RebateMonger]

On the enclosure loss... I'm quite scared of that actually.

Exactly what are you guys referring to when you say, "enclosure loss"?

 

[imagoon]

Exactly what are you guys referring to when you say, "enclosure loss"?

When stacking tons of disks many times a SAN unit will let you stack enclosures of 15 disks at a time. Basically they cable them together and you can use 45-60 disks. Enclosure loss = 1 of those cabinets bombs simulating what amounts to a 15 disk simultaneous failure. Multi-disk loss wrecks arrays. So in order to be enclosure loss safe you will basically mirror the array in some way that should 1 fail, there is enough disks to keep the system up and data intact.

Down in the workstation level, the same thing can happen if someone is cramming 15 drives in to a tower case and needs 2 power supplies to run it all. Those 2 PSU's "sorta" become like enclosures where 1 PSU dying can kill 6-8 disks making the controller drop the array.

EDIT: this might help more...

Cheaper SAN but I remember it off the top of my head:

DELL MD3000i < main brain can attach 3 more MD1000's for 4 enclosures for a total of 60 disks. Each unit has 2 PSU's / 15 disks and a chain of cables. If you have an array with 5 disks in Unit 1 and 5 disks in Unit 2 in RAID 5 and Unit 2 drops for some reason, you have a 5 disk failure that might not be recoverable without a restore from a true backup. In RAID 51 you have 2 RAID 5 arrays and they mirror each other so should unit 2 drop, unit 1 is still chugging away but the mirror is broken. When unit 2 is back up, the mirror will resync.

 

[pjkenned]

Or in SOHO terms:

Say you have external SAS ports or eSATA ports on a raid 5/6 array that spans internal and external arrays. And for example a mischevious 5 year-old finds some way to power off, stick a screwdriver in & destroy, or something of that nature that brings the external array down while the other portion of the internal array is still going. You lose all of the data.

Another example is if you have two internal 3-in-2 backplanes full of drives and one suddenly shorts or something, then you will lose your array even with raid 6 since you will suffer a 3 drive simultaneous failure.

And etc. Hopefully those overly simple examples make sense.

Again, just shows why backups are good

 

[randomlinh]

It uses folder replication to separate disks, so you have redundancy. It's not replicating on the same disk.

yes, I meant that it's basically RAID 1 for me, which isn't all that useful. I was looking for something along the lines of however Drobo's "BeyondRAID" works. I don't particularly want to just have mirroring.

All the data I'd be storing on it would be be more or less important. The critical stuff would already be backed up weekly to another drive, monthly to something at home. I'd like to do online, but I don't like how mozy works since I can't really control my backups/restores/moving of systems well/"unlimited space", and a custom s3 job would be too expensive.

dedupe isn't too useful for me, so it's not much of a consideration either.

 

[RebateMonger]

If you need more than a single hard drive to store your files, you are probably beyond anything that Mozy or S3 can do for you. It'll take eternity to upload your files.