Storage and RAID questions

[TrackZ]

Hello,

I'm looking for some Mac storage advice. I currently run a Windows-based household and will be switching to Mac. I have a Synology DS1511+ with 5x3TB HD running in SHR with 1 disk parity. That has a 1.5TB USB2.0 drive attached for selected backup. I'm not currently using an online backup service.

With the Mac shift we will have an iMac and a Macbook plus iPhones/iPads. I think I'd rather have my storage be direct connected to the iMac vs NAS. I'm looking at the the G-raid 8TB Thunderbolt device for that. I'm thinking I'd buy 2 of the G-raids to maintain a redundant copy of my data and then also subscribe to Crashplan or something for offsite backup. I'll probably also throw a Time Capsule into the mix for actual Mac system backups.

What I'm unsure of is the best way to create that redundant relationship between the 2 G-raids. The options seem to be:

1. Use Mac disk utility and do a raid 1 out of them.
2. Use a program like Chronosync to do nightly backup/syncs.

Using disk utility with raid 1 makes for continual, always running sychronization. I wonder if this would create a performance hit though. I'm mainly concerned about the software raid connection though.

Is there any way my iMac could fail or that raid could fail, it damages the array, and I do lose data? Using Chronosync seems safer in that respect as the disks are mirrored daily, yet remain operationally indepedent from each other. With the raid 1 array, can I disconnect one of the G-raids, just plug it into another machine, and access the files?

Thanks!

 

[marzer]

Hello,

What I'm unsure of is the best way to create that redundant relationship between the 2 G-raids. The options seem to be:

1. Use Mac disk utility and do a raid 1 out of them.
2. Use a program like Chronosync to do nightly backup/syncs.

Using disk utility with raid 1 makes for continual, always running sychronization. I wonder if this would create a performance hit though. I'm mainly concerned about the software raid connection though.

Is there any way my iMac could fail or that raid could fail, it damages the array, and I do lose data? Using Chronosync seems safer in that respect as the disks are mirrored daily, yet remain operationally indepedent from each other. With the raid 1 array, can I disconnect one of the G-raids, just plug it into another machine, and access the files?

Thanks!

RAID is not a backup solution. Using the two G-Raids, set one as primary storage and use Chronosync to synchronize at regular intervals to the other G-raid. That's the solution I went with for the home media library and two 2TB FW800 drives.

Nice thing about Chronosync is it will archive deleted and replaced files so if a file is mistakenly deleted or altered unexpectedly on the primary you can recover it from the backup in the future. I've had my primary drive get corrupted and simply pointed my iTunes to the synchronized backup while I recovered the primary.

[Hmmm, now that I think about it as I typed it, that wasn't smart to operate from the backup before I recovered a duplicate set ...but you get my drift.]

And then I have a Time Capsule that provides the backup location for all the computers in the house so there's no space contention on the media drives as Time Machine is known to do.

 

[kjetilbj]

I have ordered the Pegasus with 4x1 TB harddrives, planning to connect it to my macbook pro. Is it possible to set it up, so that the first 2 disks are RAID 0, and the 3 and 4 are getting synced from 1 and 2? As backup? And will this be a setup, so that it does its work at night or whenever I want?

thank you

 

[murphychris]

Is there any way my iMac could fail or that raid could fail, it damages the array, and I do lose data?

Yes. Mac OS X's file system is in the same ballpark reliability wise as NTFS. Neither are resilient file systems. Both can become irreparably corrupt if writes are occurring at the time there's a power or hardware failure. Both totally lack any kind of assurance that the data reported by the drive is actually valid - no additional error detection or correction is used.

With important data, JHFS+/X and NTFS bring nothing additional to the table in reliability beyond the built-in ECC on the disks themselves. Modern file systems are better, and at the moment you can only get them on a NAS.

But with the redundancy you're incorporating, you're probably fine except for the fact you can have corrupted data and never know it, never be informed of it, until you try to actually use the data in the file.

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Further, once corruption enters into your storage solution, it almost invariably is replicated, again without detection. In RAID 1, instantly the mirror has corrupt data. And with a syncing operation, any corrupt files are still seen as valid and are replicated to the sync'd copy. And to Time Machine. And to Crashplan.

I've moved to AF (Advanced Format) disks, because their ECC is better than non-AF disks. And I keep an eye on them with periodic long offline SMART tests using smartmontools. Unfortunately every GUI version that accesses SMART diagnostics in the drive only reports PASS/FAIL rather than the detailed attributes you need to see if there are read/write errors (recoverable or unrecoverable) or bad sectors developing. And Apple provides nothing that polls the disk for this information.

 

[FireWire2]

Fast RAID5

I would suggested this
http://eshop.macsales.com/item/DAT Optic/UF8R5J/

You can configure @ RAID5+Hot spare with the 5th drive.. this make the raid more reliable

 

[murphychris]

I would suggested this
http://eshop.macsales.com/item/DAT Optic/UF8R5J/

You can configure @ RAID5+Hot spare with the 5th drive.. this make the raid more reliable

I would disqualify RAID 5 due to the write hole. You're better off with RAID 10.

It's also worth noting that with proprietary solutions the RAID implementation is specific to the chipset/firmware. Out of warranty, hardware problems require service/replacement parts from the manufacturer in order to regain access to the data. You can't just take the drives and pop them into a totally different RAID product. Conversely open source implementations allow precisely this.