Привет. Всех с наступившим.
Ранее я создавал тему SAS или SSD. В итоге решил использовать SSD. И так имеем два Intel SSDSC2CW240A3K5. И еще два больших SATA III в software RAID-1. На сервере будет CentOS 6 + OpenVZ, SSD под VPS, SATA под бекапы. Сначала я хотел объединить два SSD в software RAID-1. Но нагуглил вот что
In addition, keep in mind that MD (software raid) does not support discards. In contrast, the logical volume manager (LVM) and the device-mapper (DM) targets that LVM uses do support discards. The only DM targets that do not support discards are dm-snapshot, dm-crypt, and dm-raid45. Discard support for the dm-mirror was added in Red Hat Enterprise Linux 6.1.
Red Hat also warns that software RAID levels 1, 4, 5, and 6 are not recommended for use on SSDs. During the initialization stage of these RAID levels, some RAID management utilities (such as mdadm) write to all of the blocks on the storage device to ensure that checksums operate properly. This will cause the performance of the SSD to degrade quickly.
Еще нагуглил это.
The big question here is /why/ would you want TRIM support? In many circumstances it leads to slower operations, and for SSDs from the past couple of years it is almost entirely superseded by the SSD's own garbage collection.
So while there certainly has been some work done on TRIM and md raid, it is not a priority as it is of questionable benefit. You might find some operations are a little faster for older SSDs if you use TRIM, but your metadata operations will be a lot slower.
Your best bet is just to make sure you only buy SSDs that are at least half decent, and don't worry about TRIM.
Как быть с TRIM? Использовать ли для зеркала LVM? Стоит ли вообще делать RAID-1 из SSD? Мб лучше сделать из них RAID-0 + частые бекапы на SATA? Спасибо за ваши советы.
