80 percent barrier

From the Intel X25-M it is known that there is a performance barrier - that's what we call it - when it is filled with up to 80 percent of its capacity or more. The following results show how the Intel X25-E Server SSD reacts when it is filled by more then 80 percent of its capacity.

Therefore we test the SSD with a blocksize of 256 KByte and a 4 GByte dump-file. Because of 256 KByte block size we can minimize the influence of the access time on the throughput. We now increase the number of active writing/reading threads one by one. Every thread active writes/reads 4 GByte of data. Finally when we have eight threads writing/reading 32 GByte of data will be written/read.

The following table recapitulates what the Intel X25-E Server SSD is capable when it isn't filled over more than 80 percent of its capacity.

The following table shows the performance after seven threads were writing/reading from the Intel X25-E SSD.

We remark a massive performance decreas in sequential writing and random reading. Sequential reading and random writing seem not to be affected.

When we analysed the raw data we generated about the access time for every single operation we can see some kind of regularity in the access time increasing. It looks like the access time is increasing slowly from between 20 and 30 microseconds to 200 and 300 microseconds and then suddenly hits a peak between 0.05 to 0.3 seconds for only one single operation! We aren't sure about this but it somehow seems that cache misses start to occur exponentially.

Low-level formatting

If there would only be the 80 percent bug - how we call it - and you would face no furhter problems when accidentally writing more than 80 percent on your SSD, you'd probably overlook this point. But unfortunately there is one annoying side effect. If you once write more than 80 percent on the SSD you afterwards need to low-level-format your Solid State Drive until you get the original performance back. Especially when you installed the operating System on an X25-E this is probably a very unconfortable fact.

If you're familiar with Linux you will have the opportunity to set all the bits on the SSD to zero using the following command: dd if=/dev/zero of=/dev/hda "hda" stands for the corresponding drive which you can look up typing "fdisk -l" in your console and pressing enter. If you don't know anything about Linux there is also a possbility to create a DOS-boot-disk with a program called Secure Erase on it. If you do so you will have to start from the bootable floppy, CD-ROM or USB drive. From there you can execute Secure Erase.