News

posted on 04 June 2008 08:20

Sun has announced that ZFS, its radical open source file system, has been optimised to use flash solid state disks (SSD) for its working file storage to produce faster file operations. It will offer SSD storage in its servers soon, but has not said it will add a tier of SSD storage to its external storage arrays.

Sun is using NAND flash technology as a cache between a server's main memory (DRAM) and hard disk drives (HDD) to get far faster file system operations; flash is being used to turbo-charge Sun's servers rather than its network-attached drive arrays. This is not a direct competitor to a flash SSD tier in EMC's Symmetrix.

What Sun has decided is that certain working files used by ZFS, the file system in the Solaris O/S, currently stored on a server's hard drives, can be processed very much faster if they are stored in flash memory because of the very much higher IOPS rate from flash. It thinks it can balance CPU IOPS and filesystem IOPS in this way.

Here's the Sun example: a quartet of quad-cored Xeons in a Sun X4450 server put out 845,000 IOPS. The channel between the X4450's DRAM and its direct-attached drive array of 8 x 146GB 10,000rpm SAS hard disk drives runs at 140,000 IOPS and the disk storage runs at 1,600 IOPS, a gross disparity leading to CPUs waiting for disk I/O.

By placing 24 SSDs in front of the SAS disks, and replacing the DRAM-storage bridge with 6 SAS 3G cards, both bridge and SSD-frontended storage run at 840,000 IOPS, a fantastic speed boost.

ZFS has two particular working storage areas that benefit from this. It has a read and write cache pool and a ZFS Intent Log (ZIL) which stores intended ZFS operations. By moving them from HDD to SSD their operation speeds up.

Sun servers will be given what it calls a hybrid storage pool with DAS (direct-attached storage) composed of a front tier of SSDs and a main tier of traditional hard drives. There will be, for example, a 32GB SSD for the ZIL store and an 80GB SSD for the read and write cache pool.

It seems pretty clear that these will be Intel SSDs (see here) although Sun's Shane Sigler, the CTO for Sun's Systems Marketing Organisation (but not Sun's chief CTO who remains Greg Papadopulos), was not willing to say so: "I can't really comment."

The interface will be SATA and not Fibre Channel: "We're not really focussed on Fibre Channel." The impression given was that SAS could effectively replace Fibre Channel anyway.

Sigler was keen to play the green card, saying that the SSDs used 2-3 watts of electricity versus the 15 watts needed by fast Seagate hard drives.

The use of SSD technology will significantly reduce the power draw needed by the many servers in high-performance computing environments as the electrically economical SSDs will replace electrically greedy hard drives. Sigler said: "It will have a pretty big input in terms of massive data centers and reduce the power footprint substantially at the same time as increasing performance."

The green story is balanced by the performance story with Sigler saying that, with SSDs: "We can get consistent latencies for IOPS which is not true for disk drives."

The benefit is not just for ZFS, Sigler said: "We'll be able to opitimize buffering for MySQL, PostGres and the Lustre File System." Flash is being used to boost Sun's open storage and open source stories.

Flashed server out later this year

Sigler said Sun will add flash to all its servers: "We're looking at shipping flash in every server before 2010 with more flash capacity than DRAM capacity. ... We're looking at actually having a system out in the second half of this year. ... We are doing a mix of work with partners as well as internally for the rollout later this year."

The X4500 Thumper server/storage hybrid system could see some of its hard drives replaced by flash SSDs to give it a performance boost.

^{[Chris Mellor.]}