IBM (reach) + XIV (technology) is the magic that provides an edge for this version of the technology over all the others.

They obviously need 120 disks to establish a fairly wide stripe width in order to guarantee some level of performance. What is their stripe width..?

Their seek patterns are random and not a lot can be done to improve i/o per sec using cache algorithms (disks already implement ‘elevated’ seeks). So…all they have left is brute force caching and this explains the very large size of cache in each disk enclosure.

Nextra datasheet shows that the cabinet contains 8 disk enclosures, i.e. their stated 120 disk minimum configuration. This means that one of the disk enclosures is a ‘spare’?
If so, then it seems that they have a ‘stripe width’ of 52 disks, with (say) 1 spare disk.
Some spare space is required on each disk …. So the useable space is at around 40% of the array capacity … and the same goes for wasted power.

It all seems to be ‘brute force’ engineering… it is hard to get impressed.

Just my gut feeling, and how I’d do it…

3Par, Compellent and others are pretty similar.

D

James…we all know about bonding . As noted above, this seems to be an X86 motherboard with 15 disk backend interface, supporting 1 Gbit iSCSI protocol, with totally random seek patterns to disks (design criteria). They will get around 5 MB per disk … but it is cheap, obvious… and probably a ‘good enough’ solution, for the time-being.

A question …. What happens if we lose a complete 15 disk chassis ?
It contains a single motherboard, not designed for hot swap. What are their repair logistics & the expected time to completely re-sync the mirrors (?).
Surely they don’t expect the customer to swap the chassis & disks. Let see how it self-heals here.

Another Question… the system is based on a minimum configuration of 160 disks. Does this mean that the stripe width is fixed ? What is required as a “minimum disk expansion increment”, in terms of hardware ?

Also, their cabling to externally connected switches must be a clutter and the number of power supplies and fans don’t add much to the overall system reliability.

The argument regarding It is very clear that such ‘commodity’ general purpose hardware, even when built for Dell, HP or IBM is based on limited production runs, constantly ‘new” chipsets and become obsolete on a yearly basis…. i.e. unsupportable throw-away replacement mentality….with all of the implications re OS, BIOS, drivers, etc.

It is easier & cheaper to design/build a high quality, reliable X86 “controller” box, with the exact hardware functionality and minimum power consumption to do the job …. much like some of the X86 Telco or computing ‘blade’ infrastructure hardware.

One would think that IBM understands this…. even if Moshe & team do not.

Yes, it sounds like 3Par’s “chunklets” too

http://www.ibm.com/developerworks/blogs/page/InsideSystemStorage?entry=spreading_out_the_re_replication

So yeah, they rebuild a failed drive onto the empty space of many other drives. Also, much of the rebuild traffic could stay inside the bricks, making the interconnect irrelevant.