storage area network abt raid

[Chris Gordon]

Yes, you destroy the RAID5 set, reconfigure the disks as a RAID10 and reformat the volumes as necessary. Of course you’ve backed up any data you have on those disks so you can restore it all later.

Sorry, but that is very much a destructive change. How RAID5 and RAID10 work are very different in what data is where.

[Bob Zelin]

I have never heard of anyone wanting to go from RAID 5 to RAID 10 – that is a big step backwards. You can do a RAID 50, or you can do a RAID 6 (or a RAID 60), but why would you want RAID 10 – for speed and a complete mirror ? It’s kind of old fashioned.

Bob Zelin

[Pradeep Kagitala]

Hi Bob Zelin

in one interview they asked me Configure RAID 5 to Raid 1+0, Raid 0+1
is it possible

[Chris Gordon]

Bob,

I’ll have to respectfully disagree with you here. Some of your challenges with a RAID5 vs a RAID10: (Note when I say RAID10, I mean a stripe across a number of mirrored disk pairs, not the other way around).
– Rebuild times. When you lose a disk in a RAID5, the rebuild on the new disk is often far more painful than a RAID10 considering you have to read ALL of the data on the RAID set and recalculate parity for all of it. With RAID10, you just have to read data from the remaining mirror disk and write it to the new disk.
– If you’re doing a lot of updates to existing files or very small file writes you may not get the advantage of the extra disk spindles when compared to a RAID10 but you pick up the parity calc and parity write.
– Updates of files on RAID5 involve a lot more IO than on a RAID10.

Conversely, there are plenty of cases where a RAID5 or RAID6 is a better solution. At work, I’m doing some disk performance testing right now and moving a 12 disk set from RAID10 to RAID6 gave me a significant performance increase (a couple hundred MB/sec) and more space for large sequential writes. This application is one almost solely writing large files to disk with no updates or noticeable random IO and I’m not too concerned about loss of disks or the array.

Now for the part I think Bob will agree with:

Like everything, which RAID is appropriate depends on the specific situation and balancing a lot of factors. The best way to really know what is best is to test different configurations with your work flow and applications. Of course this costs time/money to do. Video editing is typically characterized (at least the majority of the data) by large files sequentially written to disk (ingesting the video) and then repeated reads of those files or at least parts of them. The additional spindles available for the reads gives RAID5 or RAID6 is big advantage in performance compared to RAID10 for the same number of disks.

Chris

[Jason Myres]

I read this article a few years ago, and it introduced me to the idea that RAID 5 and 6, while popular, aren’t the end-all, be-all for everyone:

https://www.cyberciti.biz/tips/raid5-vs-raid-10-safety-performance.html

There seem to be two camps, bandwidth vs transactions, and they have almost completely opposite requirements. So, while an Xsan admin is looking for streams of ProRes, a MySQL DBA is chasing IOPS. As much as we use RAID5, in the DBA world it’s often seen as less desirable than some combination of mirrored/striped.

JM

[Bob Zelin]

my world is only number of streams of ProRes, DNxHD, etc, not MySQL DBA, so I am blinded by this (in the same way that I only use MAC’s, only because all my clients only use MAC’s – I have no issue with PC’s, but I am blinded by my client requirement).

I am also blinded by the fact that every company that we know, from Apple, to Active, to Areca, to ATTO, to LSI, etc, etc, etc, always push and promote RAID 5 and RAID 6 (and in turn 50 and 60) – where NO ONE (no host adaptor manufacturer, or reviewer like Barefeats or AMUG) ever discusses RAID 10 (or it’s variations).

just like “we” dismiss Apple’s consumer products, “our world” consists only of professional audio and video (and it’s associated businesses like digital asset management), and the rest of the world be damned.

Bob Zelin

[Chris Gordon]

Bob (and anyone else)

I’d be curious as to your experience when recovery from a disk failure in parity RAID sets (RAID5, 6 etc). Do you see overall impact to the arrays during the rebuilds? Experience additional failures during the rebuilds?

Thanks,
Chris

[Bob Zelin]

of course Chris – it’s always been like this. The drive slows down when it’s rebuilding – but you can still use it. It’s just running slower.

Bob Zelin

[Chris Gordon]

Thanks. I normally work in the world of big databases where the impact of the rebuild is often too great (affects response times too much). A big thing that is starting to change this for us is storage tiering where the array has a mix of Flash and SATA drives (and maybe some FC or SAS depending on the specific solution) and the array moves data between the two automatically. The basic idea is the blocks you hit a lot migrate toward Flash and the stuff you never really touch ends up on SATA. Then putting the SATA disks in a RAID5 (or 6) is fine since you don’t feel the impact of the rebuilds so much — its on data you don’t really ever hit. Great for databases and similar solutions with high random IO, but for big fat streams a bunch of SATA disks in a big parity RAID still seems like the best bang for the buck.

[Matt Geier]

Hi all,

In the world of Video Editing and Real Time RAID performance, stripping tends to be very bad. It’s a lot of Large I/O’s that need to go back and forth quickly on the disk, and stripping in most cases adds a lot of overhead that tends to slow down the disk performance.

In the world of Databases, I could see RAID 10 as being okay. Just so long as the data gets to and from the raids and in one piece, all should be well…..

In a RAID 5 or RAID 6 environment, you can respectively loose 1 or 2 disks, and of course things are slow in terms of bandwidth performance, but usually you can still accomplish some method of real time performance, it’s just limited performance at that….. but it’s not “down or lost” —

Speaking in terms of Real Time video on Mac OS X of course keeping in mind all of this is a variant between vendors….

Matt G