NETGEAR is aware of a growing number of phone and online scams. To learn how to stay safe click here.
Forum Discussion
Moving beyond RAID and XRAID2
Most consumer and even pro-sumer NAS boxes use a form of RAID typically RAID1 or RAID5 or something that looks very similar to these. I think one can justifiably argue that a ReadyNAS Pro with six drives and XRAID2 is basically RAID5 with the addition of the ability to grow the volume.
It has been well known now for several years that with the enormous increase in capacity of hard disks that traditional RAID schemes like RAID5 are becoming self defeating. As one very important example of this, the time it now takes to rebuild a 6 x 3TB RAID5 system will probably be longer than 24 hours and during this time your data is totally unprotected against the possibility of a second drive failure. Yes with XRAID2 you can have two redundant drives rather than one but even with this we are reaching the stage where it still takes too long and uses too much overhead.
There are now newer more advanced schemes for protecting data compared to the original RAID schemes and I am not just referring to using more redundant drives. However I get the impression no NAS type product as yet uses these advances.
It might be worth at this point reading these articles
I would say that the ReadyNAS needs to at least on the higher models i.e. Pro models, urgently look at moving to a new more advanced scheme (perhaps it could be called XRAID3).
I have outgrown a 6 x 2TB setup and have been planning to move to a 6 x 4TB setup as merely moving to 3TB drives was going to be such a small improvement. However with the problems I detail here, and the risk of a second failure during the rebuild process I would have to use 2 redundant drives to reduce the risk of data loss. This would mean I would only get an effective capacity of about 4 x 4TB (with 2 redundant drives) compared to my current effective capacity of 5 x 2TB (with 1 redundant drive) so even though I would be using disks of double the current capacity I would only get 60% extra space.
(Let the fighting begin…)
It has been well known now for several years that with the enormous increase in capacity of hard disks that traditional RAID schemes like RAID5 are becoming self defeating. As one very important example of this, the time it now takes to rebuild a 6 x 3TB RAID5 system will probably be longer than 24 hours and during this time your data is totally unprotected against the possibility of a second drive failure. Yes with XRAID2 you can have two redundant drives rather than one but even with this we are reaching the stage where it still takes too long and uses too much overhead.
There are now newer more advanced schemes for protecting data compared to the original RAID schemes and I am not just referring to using more redundant drives. However I get the impression no NAS type product as yet uses these advances.
It might be worth at this point reading these articles
- http://www.maximumpc.com/article/news/raid5_may_soon_be_obsolete (from 2008!)
http://www.zdnet.com/blog/storage/why-r ... n-2009/162 (from 2007!)
http://www.zdnet.com/the-end-of-the-rai ... 000002737/
http://wikibon.org/wiki/v/Is_RAID_Obsolete%3F
I would say that the ReadyNAS needs to at least on the higher models i.e. Pro models, urgently look at moving to a new more advanced scheme (perhaps it could be called XRAID3).
I have outgrown a 6 x 2TB setup and have been planning to move to a 6 x 4TB setup as merely moving to 3TB drives was going to be such a small improvement. However with the problems I detail here, and the risk of a second failure during the rebuild process I would have to use 2 redundant drives to reduce the risk of data loss. This would mean I would only get an effective capacity of about 4 x 4TB (with 2 redundant drives) compared to my current effective capacity of 5 x 2TB (with 1 redundant drive) so even though I would be using disks of double the current capacity I would only get 60% extra space.
(Let the fighting begin…)
4 Replies
Replies have been turned off for this discussion
jelockwood wrote:
There are now newer more advanced schemes for protecting data compared to the original RAID schemes and I am not just referring to using more redundant drives.
Such as?sphardy wrote: jelockwood wrote:
There are now newer more advanced schemes for protecting data compared to the original RAID schemes and I am not just referring to using more redundant drives.
Such as?
The third article I linked to talks about this. I don't claim to be an expert on that technology but it is clear to even normal people that RAID is not able to cope with the size of modern drives. I suppose in theory if speed had increased at the same rate as capacity has so that the time to rebuild had not grown then that would have prevented the problem. Unfortunately the speed of traditional hard disks has not grown fast enough and as a result the time to rebuild is now a danger.- In 2010 the forum collectively discussed the validity of dual redundancy (and I even linked one of the articles you referred to) -> http://www.readynas.com/forum/viewtopic.php?f=24&t=43796&p=247391. Now we explore the validity of RAID itself in our current storage climate. In perusing the third link I find a few interesting premises however my experience with FEC and dispersal (anyone remember Mango?) make me wonder how likely Netgear is to implement (and even how functional these 'larger' concepts can be in a home or SOHO environment) cutting edge technologies when we still have real issues with Samba, iTunes server, Time Machine connectivity, etc. I see value in increasing spindle count and decreasing individual element capacity (the same thing you do when you need IOPS) but the real question - who wants to pay for it? Heck, nobody was even interested in data duplication on the ReadyNAS (http://www.readynas.com/forum/viewtopic.php?f=18&t=51922&p=298006) and that, potentially and only to a certain extent - might have reduced your storage requirements and at least temporarily obviated the need for a drive upgrade (though there are those who will tell you dedupe isn't worth it without much, much more data).
I'd ask isn't it cheaper, safer and easier (in the long run) to buy a second ReadyNAS?
RAID-5 and RAID-6 are forms of dispersal, with the RAID stripes spreading the data across multiple spindles. Of course in a large data center, you have have an enormous number of spindles, and RAID-5 and RAID-6 don't really take full advantage of that. The main idea in using more modern FEC codebooks is that they allow dispersal over a massive number of spindles.jelockwood wrote: sphardy wrote: jelockwood wrote:
There are now newer more advanced schemes for protecting data compared to the original RAID schemes and I am not just referring to using more redundant drives.
Such as?
The third article I linked to talks about this. I don't claim to be an expert on that technology but it is clear to even normal people that RAID is not able to cope with the size of modern drives. I suppose in theory if speed had increased at the same rate as capacity has so that the time to rebuild had not grown then that would have prevented the problem. Unfortunately the speed of traditional hard disks has not grown fast enough and as a result the time to rebuild is now a danger.
I agree that rebuild time is an issue already, and will become worse as drive capacities increase. Another trend you didn't mention is power management. There is interest in building arrays of disks that don't require them all to be spinning to access any of the data.
So I'd agree that over time it is inevitable that the RAID formats used in data centers will continue to advance in ways that will take full advantage of the massive amount of spindles that all data centers have.
However, I don't see the applicability of these techniques to consumer storage. I think the key issue here is that 4-6 spindles really is about the most you want to put in a home NAS - so the massive dispersal idea really doesn't apply. SSDs could change the game if they become cheap enough, as they run a lot cooler and don't have the vibrational issues of hard drives.
NETGEAR Academy
Boost your skills with the Netgear Academy - Get trained, certified and stay ahead with the latest Netgear technology!
Join Us!
