The Impact of Disruptive Technologies on the Professional Storage Market
by Johan De Gelas on August 5, 2013 9:00 AM EST- Posted in
- IT Computing
- SSDs
- Enterprise
- Enterprise SSDs
NetApp: Flash Anywhere
Nutanix, CloudFounders/Amplidata, and Fusion-IO (covered on page eight) are clearly challenging the current market leaders NetApp and EMC. We decided to take a closer look at how the giants respond by looking at the latest products of NetApp. NetApp's first step with using flash memory was called “flash cache”. NetApp simply added a PCIe flash card and inserted it into its FAS V6200 storage arrays.
It was a quick way of adding some performance, but it was far from exploiting the true potential of NAND memory. First of all, the flash cache was only used for reads and secondly the cache used a very simple but hardly efficient FIFO eviction algorithm. Case studies (done by NetApp Customers) with applications with a typical read/write mix reported about 30% more IOPs and on average 20% lower response times when arrays with 10K RPM SAS disks where replaced by an array with a massive flash cache and slightly slower 7200 RPM disks.
Considering how large the gap is between flash memory and magnetic disks, and the small gap between 10K and 7.2K RPM disks, that is rather underwhelming. Part of the reason is of course that these arrays already have a healthy amount (4-8GB) of NVRAM (Non Volatile RAM) that caches the hottest data and makes writes more sequential. However, the list price of a flash cache module is anywhere between $16000 (256GB) and $50000 (1TB).
In a published benchmark, six FAS6240 with 192 15K RPM disks (costing $1.5 million in total!) achieved about 250k IOPs, or about 40K IOPs per array. To sum it up: it's a very high premium for an underwhelming but very welcome performance boost. Only customers who use read dominated applications (like warehouse / OLAP app) can really expect excellent performance.
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jhh - Wednesday, August 7, 2013 - link
And Advanced/SDDC/Chipkill ECC, not the old-fashioned single-bit correct/multiple bit detect. The RAM on the disk controller might be small enough for this not to matter, but not on the system RAM.tuxRoller - Monday, August 5, 2013 - link
Amplidata's dss seems like a better, more forward looking alternative.Sertis - Monday, August 5, 2013 - link
The Amplistore design seems a bit better than ZFS. ZFS has a hash to detect bit rot within the blocks, while this stores FEC coding that can potentially recover the data within that block without calculating it based on parity from the other drives on the stripe and the I/O that involves. It also seems to be a bit smarter on how it distributes data by allowing you to cross between storage devices to provide recovery at the node level while ZFS is really just limited to the current pool. It has various out of band data rebalancing which isn't really present in ZFS. For example, add a second vdev to a zpool when it's 90% full and there really isn't a process to automatically rebalance the data across the two pools as you add more data. The original data stays on that first vdev, and new data basically sits in the second vdev. It seems very interesting, but I certainly can't afford it, I'll stick with raidz2 for my puny little server until something open source comes out with a similar feature set.Seemone - Tuesday, August 6, 2013 - link
Are you aware that with ZFS you can specify the number of replicas each data block should have on a per-filesystem basis? ZFS is indeed not very flexible on pool layout and does not rebalance things (as of now), but there's nothing in the on-disk data structure that prevent this. This means it can be implemented and would be applicable on old pools in a non disruptive way. ZFS, also, is open source, its license is simply not compatible with GPLv2, hence ZFS-On-Linux separate distribution.Brutalizer - Tuesday, August 6, 2013 - link
If you want to rebalance ZFS, you just copy the data back and forth and rebalancing is done. Assume you have data on some ZFS disks in a ZFS raid, and then you add new empty discs, so all data will sit on the old disks. To spread the data evenly to all disks, you need to rebalance the data. Two ways:1) Move all data to another server. And then move back the data to your ZFS raid. Now all data are rebalanced. This requires another server, which is a pain. Instead, do like this:
2) Create a new ZFS filesystem on your raid. This filesystem is spread out on all disks. Move the data to the new ZFS filesystem. Done.
Sertis - Thursday, August 8, 2013 - link
I'm definitely looking forward to these improvements, if they eventually arrive. I'm aware of the multiple copy solution, but if you read the Intel and Amplistore whitepapers, you will see they have very good arguments that their model works better than creating additional copies by spreading out FEC blocks across nodes. I have used ZFS for years, and while you can work around the issues, it's very clear that it's no longer evolving at the same rate since Oracle took over Sun. Products like this keep things interesting.Brutalizer - Tuesday, August 6, 2013 - link
Theory is one thing, real life another. There are many bold claims and wonderful theoretical constructs from companies, but do they hold up to scrutiny? Researchers injected artificially constructed errors in different filesystems (NTFS, Ext3, etc), and only ZFS detected all errors. Researchers have verified that ZFS seems to combat data corruption. Are there any research on Amplistore's ability to combat datacorruption? Or do they only have bold claims? Until I see research from a third part, independent part, I will continue with the free open source ZFS. CERN is now switching to ZFS for tier-1 and tier-2 long time term storage, because vast amounts of data _will_ have data corruption, CERN says. Here are research papers on data corruption on NTFS, hardware raid, ZFS, NetApp, CERN, etc:http://en.wikipedia.org/wiki/ZFS#Data_integrity
For instance, Tegile, Coraid, GreenByte, etc - are all storage vendors that offers PetaByte Enterprise servers using ZFS.
JohanAnandtech - Tuesday, August 6, 2013 - link
Thanks, very helpful feedback. I will check the paper outmikato - Thursday, August 8, 2013 - link
And Isilon OneFS? Care to review one? :)bitpushr - Friday, August 9, 2013 - link
That's because ZFS has had a minimal impact on the professional storage market.