The SSD Anthology: Understanding SSDs and New Drives from OCZ
by Anand Lal Shimpi on March 18, 2009 12:00 AM EST- Posted in
- Storage
OCZ Tries Again with the Vertex
This is Ryan Petersen:
He’s the CEO of OCZ Technology. He wasn’t too happy after my Intel X25-M SSD review.
Although that review was about the X25-M, it addressed a major shortcoming with a number of other SSDs in the market - the most popular at the time being OCZ’s Core line.
The problem with the Core line was that although they were competitively priced, they had a major performance issue: small file write latency. The problem manifested itself in system-wide stuttering during disk intensive multitasking. It wouldn’t take a lot to make those drives stutter, and until that article went live, everyone assumed that the problem was Windows, the disk controller, or something else.
I placed the blame on the drives and Ryan wasn’t all too happy.
We argued. A lot. He claimed it was unfair that I was comparing the Core series to Intel’s far more expensive X25-M; I argued that the user experience offered by his drives was inferior to that of a regular hard drive. We never really saw eye to eye on SSDs after that article.
Ryan told me the problem was a lack of cache, and that they’d have a future version of their SSD with a large off-chip DRAM cache. Ryan did not want to send me any more SSDs that didn’t have a cache on them. It wasn’t just OCZ, we had difficulty getting JMicron based SSDs from most manufacturers after that article. Manufacturers were pissed.
I offered to look at any new SSDs they had coming, regardless of who made the controller. But I made one thing very clear - I did not believe that the JMicron based drives were fit for sale. I felt that they were hurting the image of SSDs in the market and doing more harm than good. Ask any of the major players in the flash and OS industries and you’ll hear the same complaint. We need good SSDs in the market, not a mixture of great ones and bad ones.
In early December I got word from OCZ that their first drive with a DRAM cache was nearing final production. The controller was from a Korean company called Indilinx, with a number of ex-Samsung engineers. JMicron was out for this product, they didn’t have a suitable controller - the JMF602B was it. I won’t draw too much attention to the fact that if the JMF602B drives were indeed fine then there would be no need to consider another controller manufacturer.
The Indilinx Barefoot controller would support up to 64MB of off-chip DRAM, but have no on-die cache. All user data would be buffered in this memory. Now 64MB is more than enough to handle anything being written to the drive, but the memory is also used for the ARM7 based processor for its work in dealing with wear leveling and flash block cleaning (removing invalid pages).
There’s a key distinction here between the Barefoot and Intel’s controller - the X25-M doesn’t store any user data in its DRAM. Technically the Barefoot approach is no less prone to dataloss than a standard hard drive, but the Intel approach is a bit better. In the event of sudden power loss there’s a chance that some of the data in the Barefoot’s 64MB buffer could be lost before it’s committed to flash.
The OCZ Vertex drive would have a more heavy duty controller, with an ARM processor and a large off-chip DRAM to improve performance. To top it all off, OCZ would sell it at a price much lower than Intel’s X25-M. Could this finally be the affordable SSD we’ve been looking for?
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punjabiplaya - Wednesday, March 18, 2009 - link
Great info. I'm looking to get an SSD but was put off by all these setbacks. Why should I put away my HDDS and get something a million times more expensive that stutters?This article is why I visit AT first.
Hellfire26 - Wednesday, March 18, 2009 - link
Anand, when you filled up the drives to simulate a full drive, did you also write to the extended area that is reserved? If you didn't, wouldn't the Intel SLC drive (as an example) not show as much of a performance drop, versus the MLC drive? As you stated, Intel has reserved more flash memory on the SLC drive, above the stated SSD capacity.I also agree with GourdFreeMan, that the physical block size needs to be reduced. Due to the constant erasing of blocks, the Trim command is going to reduce the life of the drive. Of course, drive makers could increase the size of the cache and delay using the Trim command until the number of blocks to be erased equals the cache available. This would more efficiently rearrange the valid data still present in the blocks that are being erased (less writes). Microsoft would have to design the Trim command so it would know how much cache was available on the drive, and drive makers would have to specifically reserve a portion of their cache for use by the Trim command.
I also like Basilisk's comment about increasing the cluster size, although if you increase it too big, you are likely to be wasting space and increasing overhead. Surely, even if MS only doubles the cluster size for NTFS partitions to 8KB's, write cycles to SSD's would be reduced. Also, There is the difference between 32bit and 64bit operating systems to consider. However, I don't have the knowledge to say whether Microsoft can make these changes without running into serious problems with other aspects of the operating system.
Anand Lal Shimpi - Wednesday, March 18, 2009 - link
I only wrote to the LBAs reported to the OS. So on the 80GB Intel drive that's from 0 - 74.5GB.I didn't test the X25-E as extensively as the rest of the drives so I didn't look at performance degradation as closely just because I was running out of time and the X25-E is sooo much more expensive. I may do a standalone look at it in the near future.
Take care,
Anand
gss4w - Wednesday, March 18, 2009 - link
Has anyone at Anandtech talked to Microsoft about when the "Trim" command will be supported in Windows 7. Also it would be great if you could include some numbers from Windows 7 beta when you do a follow-up.One reason I ask is that I searched for "Windows 7 ssd trim" and I saw a presentation from WinHEC that made it sound like support for the trim command would be a requirement for SSD drives to meet the Windows 7 logo requirements. I would think if this were the case then Windows 7 would have support for trim. However, this article made it sound like support for Trim might not be included when Windows 7 is initially released, but would be added later.
ryedizzel - Thursday, March 19, 2009 - link
I think it is obvious that Windows 7 will support TRIM. The bigger question this article points out is whether or not the current SSDs will be upgradeable via firmware- which is more important for consumers wanting to buy one now.Martimus - Wednesday, March 18, 2009 - link
It took me an hour to read the whole thing, but I really enjoyed it. It reminded me of the time I spent testing circuitry and doing root cause analysis.alpha754293 - Wednesday, March 18, 2009 - link
I think that it would be interesting if you were to be able to test the drives for the "desktop/laptop/consumer" front by writing a 8 GiB file using 4 kiB block sizes, etc. for the desktop pattern and also to test the drive then with a larger sizes and larger block size for the server/workstation pattern as well.You present some very very good arguments and points, and I found your article to be thoroughly researched and well put.
So I do have to commend you on that. You did an excellent job. It is thoroughly enjoyable to read.
I'm currently looking at a 4x 256 GB Samsung MLC on Solaris 10/ZFS for apps/OS (for PXE boot), and this does a lot of the testing; but I would be interested to see how it would handle more server-type workloads.
korbendallas - Wednesday, March 18, 2009 - link
If The implementation of the Trim command is as you described here, it would actually kind of suck."The third step was deleting the original 4KB text file. Since our drive now supports TRIM, when this deletion request comes down the drive will actually read the entire block, remove the first LBA and write the new block back to the flash:"
First of all, it would create a new phenomenon called Erase Amplification. This would negatively impact the lifetime of a drive.
Secondly, you now have worse delete performance.
Basically, an SSD 4kB block can be in 3 different states: erased, data, garbage. A block enters the garbage state when a block is "overwritten" or the Trim command marks the contents as invalid.
The way i would imagine it working, marking block content as invalid is all the Trim command does.
Instead the drive will spend idle time finding the 512kB pages with the most garbage blocks. Once such a page is found, all the data blocks from that page would be copied to another page, and the page would be erased. Doing it in this way maximizes the number of garbage blocks being converted to erased.
alpha754293 - Wednesday, March 18, 2009 - link
BTW...you might be able to simulate the drive as well using Cygwin where you go to the drive and run the following:$ dd if=/dev/random of=testfile bs=1024k count=76288
I'm sure that you can come up with fancier shell scripts and stuff that uses the random number generator for the offsets (and if you really want it to work well, partition it so that when it does it, it takes up the entire initial 74.5 GB partition, and when you're done "dirtying" the data using dd and offset in a random pattern, grow the partition to take up the entire disk again.)
Just as a suggestion for future reference.
I use parts of that to some (varying) degree for when I do my file/disk I/O subsystem tests.
nubie - Wednesday, March 18, 2009 - link
I should think that most "performance" laptops will come with a Vertex drive in the near future.Finally a performance SSD that comes near mainstream pricing.
Things are looking up, if more manufacturers get their heads out of the sand we should see prices drop as competition finally starts breeding excellence.